Level 19: Caverns of Ooze

Named for the primordial ooze that flows through its naturally formed tunnels and chambers, this cavernous level of Undermountain is designed for four 15th-level characters. Those who overcome its challenges should reach 16th level. Whimsical even by Undermountain’s standards, the Caverns of Ooze offer DMs the rare opportunity to sing, should they wish to portray the genies on this level in the vein of characters from an animated feature film.

What Dwells Here?

Halaster bound two genies to this level and pitted them against one another. The Mad Mage also captured a spelljamming vessel and deposited it here, along with its crew. Finally, the demented followers of an evil god of oozes and slimes make their home here.

Genies of Earth and Water

A dao and a marid live here, having struck bargains with Halaster to rid level 20 of the lich Ezzat. The genies compete with one another. Whichever one obtains the lich’s phylactery wins its freedom, damning the other to spend the remainder of its existence in Undermountain. By the rules of Halaster’s game, the genies can use adventurers to get the job done, but they can’t cause bodily harm to one another, either directly or indirectly. A disgruntled mud mephit named Urm has been forced to act as the genies' go-between.

Scavenger Crew

The Mad Mage captured a spacefaring pirate ship called the Scavenger, stole the magic device that propels it, and left the derelict vessel and its crew to rot in the Caverns of Ooze. The ship’s mind flayer captain (see “area Captain N’ghathrod") was forced to eat the brains of several shipmates to survive. The remainder of the crew fled into the caverns and have taken refuge in the ooze-filled caverns around the ship. Now the illithid waits for new humanoid brains to deliver themselves into its waiting tentacles.

Worshipers of Ghaunadaur

The Caverns of Ooze have, at various times, served as a temple and sanctuary for worshipers of Ghaunadaur, the evil god of oozes, slimes, and other subterranean horrors. Halaster rewards these mad zealots by transforming them into oozes that retain most of their memories and intelligence. These servants of Ghaunadaur believe the god himself has blessed them. The Mad Mage does nothing to discourage this impression.

Followers of Ghaunadaur whom Halaster lures to Undermountain invariably visit a floating orb that weeps primordial ooze in area area 4. The orb is thought to be part of Ghaunadaur himself. His worshipers sometimes refer to the object as the Weeping Eye. In truth, Halaster found the oozing orb and brought it here solely to flood the caverns and mislead Ghaunadaur’s vile devotees.

Wandering Monsters

Most of the ooze that flows through this level is harmless elemental waste, but this level is also home to meandering Ghaunadaur worshipers and orog space pirates looking for food. You can use the following encounters to harry restless or resting adventurers.

Huge Gray Ooze

The characters encounter six Ghaunadaur-worshiping duergar who were transformed by Halaster’s magic into a single gray ooze with a challenge rating of 8 (3,900 XP) and these changes:

• The ooze is Huge, with 152 (16d12 + 48) hit points and a Strength score of 18.
• As an action, it can make two attacks with its pseudopods (+7 to hit). On a hit, a pseudopod deals 21 (6d6) acid damage, or 42 (12d6) acid damage while the ooze is enlarged.
• The ooze has the Enlarge and Invisibility traits below.

Enlarge (Recharges after a Short or Long Rest)

For 1 minute, the ooze magically increases in size. While enlarged, the ooze is Gargantuan, doubles its damage dice with its pseudopod attack, and makes Strength checks and Strength saving throws with advantage.

Invisibility (Recharges after a Short or Long Rest)

The ooze magically turns invisible for up to 1 hour until it attacks, it uses its Enlarge, or its concentration is broken (as if concentrating on a spell).

Intelligent Black Puddings

The characters encounter two Ghaunadaur-worshiping drow who were transformed by Halaster’s magic into Black Pudding, with these changes:

• The black puddings understand Elvish and Undercommon, but can’t speak.
• Each pudding has an Intelligence of 14 and the following Innate Spellcasting trait:

Innate Spellcasting

The pudding’s spellcasting ability is Intelligence (spell save DC 12, +4 to hit with spell attacks). It can cast the following spells, requiring no components:

At will: dancing lights, mage hand

3/day each: darkness, faerie fire, shield

1/day: Melf’s acid arrow

Space Orogs

The characters encounter 1d4 + 1 Orog hunting for easy prey. These orogs were raised in deep caverns on H’catha, a wheel-shaped planet ruled by beholders and the farthest world from Toril’s sun. The orogs wear bucket helms resembling bulbous mind flayer heads, with large, glass-covered eye holes and tentacle-like breathing tubes.

In addition to its armor and weapons, each orog carries a tangler grenade. The orogs use these grenades to restrain foes before charging into melee.

Tangler Grenades

A tangler grenade is an alchemical, nonmagical item with an ovoid resin shell that shatters on impact. An as action, a creature can throw a tangler grenade at a point up to 60 feet away. Each creature within 10 feet of a shattered tangler grenade must succeed on a DC 15 Dexterity saving throw or be restrained by sticky white webs. As an action, a creature can try to free itself or another creature within its reach from the webs, doing so with a successful DC 20 Strength (Athletics) check. A gallon of alcohol dissolves the webs produced by a single tangler grenade. Otherwise, the webs dissolve on their own after 1 hour, freeing any creatures restrained by them.

Exploring This Level

The following encounters are keyed to map 19. Many of the caverns and tunnels are natural formations, while purple worms dug others long ago. The ooze that flows through much of the level smells foul but is harmless (see the “Elemental Ooze” sidebar).

Elemental Ooze

The orb in area area 4 weeps a steady stream of ooze channeled from the Swamp of Oblivion, the border realm between the Elemental Planes of Earth and Water. This ooze is a thick, viscid brown effluvium with streaks of orange, green, yellow, and black. It smells like rotten eggs and sticks to anything it touches. The ooze is never more than 5 feet deep in any given location and is difficult terrain. It moves slowly in the direction indicated by the wavy arrows on map 19 and also behaves like it’s alive, occasionally extruding harmless pseudopods or amorphous shapes that bear passing resemblances to familiar creatures.

1. The Resplendent Grotto of Ichthyglug the Voluminous

Halaster has used his magic to tailor these caves to the satisfaction of Ichthyglug the marid.

1a. Shipwreck

This 50-foot-high cavern contains the wreck of a cog (a 54-foot-long cargo vessel with a single mast). The wreck’s features are as follows:

Hull. The ship has broken in half, the shattered bow aiming northward and the aft section leaning against the east wall. The oak hull is soft and waterlogged, as though the vessel has been underwater for years, and both halves are encrusted with barnacles.

Mast and Anchor. The mast and anchor have broken off and lie in the middle of the cave, with the mast pointing toward a shimmering curtain of water to the west.

No Sails, No Rigging, No Crew. The ship’s square sail, rigging, and crew are all missing. (The sail and the rigging disintegrated long ago.)

Characters who search the wreck discover its name carved over the barnacle-encrusted rudder: the Blue Opal. A character who learns the ship’s name and succeeds on a DC 20 Intelligence (History) check recalls that the Blue Opal sank in Waterdeep’s harbor a few years ago under mysterious circumstances, and that the crew was rescued by merfolk who live in the harbor. Armed with this knowledge, a character can examine the hull for signs of foul play and, with a successful DC 15 Intelligence (Investigation) check, discover a square, smooth-cut hole in the aft section below what would have been the water line. A successful DC 16 Intelligence (Arcana) check confirms that a disintegrate spell made the square hole, but there’s no way to know who cast the spell or why the ship was sunk.

If more than one character enters the aft section at the same time, the partial hull shifts under the added weight, topples to one side, and collapses in on itself with a thunderous racket. Any creature inside the aft section when it collapses must make a DC 15 Dexterity saving throw, taking 22 (4d10) bludgeoning damage from falling debris on a failed save, or half as much damage on a successful one. The watery curtains in area area 1b prevent the sound of the collapse from reaching area area 1c.

1b. Curtains of Water

This passage has a 20-foot-high, arched ceiling and contains three 1-foot-thick, magic curtains of translucent, shimmering green seawater. Each watery curtain stretches from floor to ceiling and wall to wall. Sound passing through a curtain is greatly reduced; only creatures within 5 feet of it can hear anything from the other side.

Any object thrown or shot through a watery curtain has a cost of 60 feet immediately applied to its distance traveled. If this added distance changes a ranged weapon attack from normal to long range, the attack roll is made with disadvantage. An object that enters the curtain and can travel no farther falls to the floor inside the curtain.

Spell effects that would not reasonably pass through the watery curtain are stopped by the barrier as though it were a solid wall. For example, a magic missile spell could pass through the curtain to hit creatures on the far side of it, but the explosion from a fireball spell would not get through the barrier.

A creature that passes through a watery curtain gets drenched but suffers no other ill effects. In addition, lit torches and other open flames of a nonmagical nature are doused as they pass through the water. Any creature that takes damage from water, such as a fire elemental, takes 11 (2d10) cold damage when it starts its turn in a watery curtain or enters it for the first time on a turn.

If a watery curtain takes 50 cold damage or more from a single source, it becomes a 1-foot-thick wall of ice (as if created by a wall of ice spell) for 10 minutes before reverting to its original form. A watery curtain targeted by a successful dispel magic spell (DC 17) is destroyed for good.

1c. Ichthyglug’s Cavern

Music. Magical harp music fills this 30-foot-high cavern.

Pool. A 15-foot-deep freshwater pool is home to a marid and six Swarm of Quippers.

Walls. The damp walls have harmless snails and giant starfish clinging to them.

The marid, Ichthyglug, is swimming in his pool when the characters first arrive. He greets them with a song (see the “area Ichthyglug’s Song” sidebar). As he sings, Ichthyglug uses his magic to cause fountains of water to erupt from the pool as quippers leap out of the water around him. Ichthyglug is neither good nor evil, but always unpredictable. His attitude toward the characters reflects their attitude toward him.

After concluding his song, Ichthyglug floats up to characters who seem receptive and gives them the opportunity to flatter his singing. After these pleasantries, he offers the characters a quest: destroy the lich Ezzat on level 20 and give the lich’s phylactery to Ichthyglug. The marid promises fabulous treasure in exchange, even going so far as to mention that he is forced by Halaster’s magic to make good on this promise (see “Treasure” below).

If the characters complete Ichthyglug’s quest and give Ezzat’s phylactery to the marid, the pool in this cavern turns into a vortex that draws Ichthyglug, the water, the quippers, and the lich’s phylactery back to the Elemental Plane of Water. The characters find Ichthyglug’s promised reward at the bottom of the drained pool. Characters who complete Ichthyglug’s quest should receive XP as if they had defeated the marid and the swarms of quippers in combat.

If the characters destroy Ezzat but give the lich’s phylactery to Jarûk the dao in area area 11b, Ichthyglug knows this. Furious, he attacks the characters the next time he sees them.

Ichthyglug can’t leave his cave without Ezzat’s phylactery. If the marid dies here, his body disintegrates into a burst of water and foam, only to re-form 24 hours later. (The characters don’t receive XP for killing Ichthyglug more than once.)

The marid commands the quippers to attack anyone who dares to enter his pool. The swarms pose no danger to creatures on land.

Treasure

Ichthyglug wears a pair of golden bracers shaped like octopi (250 gp each) and a large silk vest studded with ten blue spinels (500 gp each). These baubles vanish with the marid when he returns to the Elemental Plane of Water.

Ichthyglug’s reward consists of a suit of mariner’s armor (scale mail) and two common wondrous items: a candle of the deep and a pole of angling (both described below). These items appear only after the characters complete Ichthyglug’s quest and help the marid escape from Undermountain.

The flame of the candle of the deep is not extinguished when immersed in water. It gives off light and heat like a normal candle.

The pole of angling looks like a 10-foot pole. While holding the pole, one can speak the command word (“Ichthyglug”) and transform it into a fishing pole with a hook, a line, and a reel. Speaking the command word again changes the fishing pole back into a normal 10-foot pole.

2. Space Orogs

Eyes. The 15-foot-high ceiling of this passage is carved with hundreds of glaring eyes. (Halaster used magic to create the eyes, which are harmless.)

Orogs. Twelve hostile Orog (see “area Space Orogs") are camped here. Subtract from this number any orogs previously encountered and defeated as wandering monsters.

One of the orogs has 60 hit points and is bigger than the others. Her name is Rukha, and until recently she served as first mate aboard the Scavenger (see area area 13).

Treasure

Rukha the orog has a sending stones tucked in one of her gauntlets. Rukha’s mate, the former cook of the Scavenger, had the matching stone but lost it (see area area 13c).

3. Ooze There?

The characters see odd shapes form out of the ooze that flows nearby.

3a. The Great Ooze March

The river of ooze flows north through this 15-foot-high cave (see “area Elemental Ooze"). When the characters first arrive, the ooze rises and takes the form of a conga line of modrons stretching as far as the characters can see. The modrons march against the sluggish flow and make little progress. After 1 minute, they sink back into the ooze. The ooze modrons aren’t creatures or spell effects, and they can’t be harmed or dispelled.

3b. Ooze Halaster

An artery of ooze flows down this tunnel and pools in a slight depression in the rocky floor. The first time anyone comes within 10 feet of the pool, the ooze rises up, takes the form of Halaster Blackcloak, and flails its arms in a way that suggests it might be trying to cast a spell. After 1 minute, the effigy of Halaster loses its form and becomes a pool of ooze once more. The ooze isn’t a creature and can’t be harmed, nor is it a magical effect that can be dispelled.

4. The Weeping Eye

Ooze. This 60-foot-high cavern contains a large pool of viscid, foul-smelling ooze that flows sluggishly northwest.

Urm. A mud mephit named Urm crouches near the edge of the ooze (at the spot marked M on map 19), absently poking it with a short pole while mumbling to itself.

Orb. Near the east wall, a 10-foot-diameter orb of ooze floats 5 feet above the pool. The orb weeps a continuous stream of ooze into the pool and appears to be its source (see “area Orb of Ooze” below).

Rock Formations. The cavern’s ceiling is dotted with stalactites, and the ooze flows around a few stalagmites that rise from the rocky floor.

Urm had the misfortune of being caught up in the ooze being siphoned from the Swamp of Oblivion and deposited here. Halaster found the mud mephit and cast a geas spell on it, compelling it to serve Jarûk the dao and Ichthyglug the marid. The genies use Urm as an intermediary to communicate insults to one another, but the mephit has grown weary of the genies' game. It wants to be free of Halaster’s geas spell.

Urm knows all about the competition between Jarûk and Ichthyglug, and tries to lead adventurers to both genies, one after the other. Urm offers to take characters to see Ichthyglug first (area area 1), since the marid is closer. If the characters have already spoken with Ichthyglug, Urm offers to guide them to Jarûk’s caverns (area area 11) by following the river of ooze.

Urm is lazy and selfish, inclined not to help characters beyond what it must do to satisfy the terms of its geas spell. It is familiar with the dangers lurking in the Caverns of Ooze but denies knowing anything. Removing Halaster’s geas spell makes the mephit somewhat more helpful but doesn’t change its wicked disposition. In exchange for its newfound freedom, Urm shares the following information, which is a mixture of truth and lies:

• The ooze that spills from the orb and fills these caverns comes from a place called the Swamp of Oblivion (true).
• Halaster captured a strange-looking vessel and hid it in a giant cavern nearby (true). The ship is alive (false).
• A powerful demon is trapped in a statue to the north (false).

Orb of Ooze

The orb is immobile, though it can be moved with a telekinesis spell or similar magic. Casting a disintegrate spell on the orb destroys it and stops the flow of ooze into the cavern. Other spells have no effect on the orb.

Creatures and objects can pass through the orb, which is made of the same ooze found throughout this level of the dungeon. Any creature that enters the orb is restrained by it. A creature restrained by the orb can use an action to make a DC 15 Strength (Athletics) or Dexterity (Acrobatics) check, freeing itself on a success. Another creature outside the orb can use an action to attempt the check if its within reach of the restrained creature; on a successful check, the creature is freed from the orb.

5. In the Grip of Ghaunadaur

A 15-foot-high tunnel containing an open pit connects two caves with 20-foot-high ceilings.

5a. Pudding Pit

This naturally formed pit is 20 feet across and 20 feet deep. At the bottom of the pit are three intelligent black puddings (see “area Intelligent Black Puddings") that used to be drow worshipers of Ghaunadaur. When they detect prey nearby, the puddings climb the sides of the pit and use faerie fire spells to outline their intended targets before attacking with their pseudopods. The puddings cast Melf’s acid arrow spells at prey beyond their reach.

5b. Standing Gate to Level 12

At the north end of this 20-foot-high cave are two 15-foot-tall standing stones hewn from black basalt. Carved into the lintel spanning them is a large, blood-red X. The standing stones form one of Halaster’s magic gates (see “area Gates").

When a creature comes within 5 feet of the gate, rivulets of blood begin to seep from the rocky pores of the standing stones. The rules of this gate are as follows:

• The gate opens for 1 minute if a creature marked with a bloody X stands within 5 feet of it.
• Characters must be 12th level or higher to pass through this gate (see “area Jhesiyra Kestellharp"). The first creature to pass through the gate triggers an elder rune (see “area Elder Runes").
• A creature that passes through the gate appears in area area 8b on level 12, in the closest unoccupied space next to the identical gate located there.

6. Cave with a View

Stalactites. A few stalactites cling to this cavern’s 30-foot high, domed ceiling.

Vessel. An enormous vessel is clearly visible through openings in the northwest wall (see area area 13).

7. Standing Gate to Level 21

Rubble. The floor of this 20-foot-high cave is strewn with stony rubble that acts as difficult terrain.

Fake Beholder. A gas spore, easily mistaken for a beholder, floats near a pair of 15-foot-tall menhirs made of semitransparent crystal. Imprisoned inside each menhir is a sleeping nalfeshnee, its leathery wings wrapped tightly around its head and body.

The gas spore drifted into this cave from area area 8. Its spores contain memory fragments of the dead beholder that birthed it. A creature that inhales the spores inherits a random memory, determined by rolling on the Beholder Memories table. These memories are experienced from the eye tyrant’s point of view.

Beholder Memories

Nalfeshnees

The sleeping demons can’t be targeted by spells or attacks while trapped inside the crystal menhirs. They remain asleep until awakened (see “Standing Gate” below). An awakened nalfeshnee teleports out of its menhir and attacks, then returns to slumber in its menhir when there are no more enemies in sight.

Standing Gate

The crystal menhirs are indestructible and form one of Halaster’s magic gates (see “area Gates"). Striking either menhir with a hard object or targeting it with a shatter spell deals no damage but causes the standing stone to ring loudly, awakening the demon inside. Nothing else causes these demons to awaken. While outside its menhir, a nalfeshnee can be magically compelled to divulge the command word that activates the gate. A legend lore spell or similar magic also reveals the command word. The current word is “Kelserath,” but Halaster changes it every few days.

The rules of this gate are as follows:

• The gate opens for 1 minute if a creature speaks the proper command word within 10 feet of it.
• Characters must be 16th level or higher to pass through this gate (see “area Jhesiyra Kestellharp"). The first creature to pass through the gate triggers an elder rune (see “area Elder Runes").
• A creature that passes through the gate appears in area area 23b on level 21, in the closest unoccupied space next to the identical gate located there.

8. Thanks for the Memories

Ceiling. This cavern has a 30-foot-high ceiling.

Gas Spores. Three Gas Spore float above a large sinkhole surrounded by rubble. Another ten Gas Spore float inside the sinkhole, which plunges 100 feet into darkness. (At the bottom of the sinkhole lies a moldering beholder corpse.)

Elevated Tunnel. A 10-foot-diameter tunnel in the west wall can be reached by climbing a 10-foot-high ledge. (This ledge is further described in area area 9.)

Halaster killed a beholder that sought to carve out a domain on this level. From its moldering corpse grew a host of gas spores. Inspection of the remains accompanied by a successful DC 15 Intelligence (Medicine) check reveals that the beholder died from fire, force, and necrotic damage. Inspection also reveals a treasure (see “Treasure” below).

The gas spores carry the memories of the beholder that birthed them. A creature that inhales the spores inherits a random beholder memory, determined by rolling on the Beholder Memories table. These memories are experienced from the eye tyrant’s point of view.

The walls of the sinkhole have abundant handholds and can be scaled with a successful DC 10 Strength (Athletics) check.

Treasure

The dead beholder has a gold tongue stud set with a peridot (750 gp).

9. High Ground

This 30-foot-high cavern contains two 10-foot ledges—a smaller one to the west and a bigger one to the south. Five Gargoyle perch on the north ledge. When the gargoyles detect intruders, one of them flies north to warn the dao (in area area 11) that visitors have arrived. If this gargoyle is wounded or waylaid, all the gargoyles attack. Otherwise, the gargoyles that remain speak to visitors in Terran, welcoming them to the “magnificent subterranean domain of Jarûk the dao.” They hurl mean insults at the characters if they don’t seem to comprehend what the gargoyles are saying.

Treasure

A gargoyle that dies but isn’t disintegrated outright falls to stony pieces, revealing a fist-sized, transparent red garnet (500 gp) where its heart used to be.

10. Culvert

The normally sluggish river of ooze flows a bit faster as it approaches a natural, 10-foot-diameter culvert in the north wall. Any creature in the ooze that ends its turn in the culvert must succeed on a DC 15 Strength saving throw or be irresistibly pulled under. Unless the creature is tethered to something, it drowns in ooze as it is borne deep into the Underdark.

11. The Glittering Caverns of Jarûk the Prismatic

These crystal-lined caves are home to a dao and its minions.

11a. Fortune Favors the Boulders

Columns and Crystals. Two columns of rock support the 30-foot-high ceiling of this cave, the walls of which are encrusted with crystals that catch and reflect light.

Boulders. The floor is strewn with boulders and rubble. Six galeb duhr beholden to Jarûk hide here, disguised as boulders.

Music. Dissonant music emanates from a smaller cave to the southeast (area area 11b).

If the characters attack Jarûk in area area 11b, the galeb duhr attack the characters when they return to this cave. Otherwise, the creatures remain motionless and pose no danger. If provoked into attacking, the galeb duhr animate boulders. The galeb duhr and their boulders can pursue prey beyond the confines of this cavern.

11b. Jarûk’s Cavern

Music. Rock music fills this 30-foot-high cavern, which resembles the inside of a geode. The walls and ceiling are encrusted with crystals that catch and reflect light.

Dao in the Sand. The floor is concave and filled with golden sand to a depth of 10 feet. A dao hides in the sand until visitors appear.

Medusas. Two Medusa wearing black robes and veils lurk in the northern alcove.

The dao, Jarûk, rises out of the sand when the characters first arrive. He greets them with a song (see the “Jarûk’s Song” sidebar). As he sings, the veiled medusas emerge from their alcove and begin to dance around him as the sand swirls and forms little dust devils. Jarûk is evil and cruel, but his current predicament motivates him to be a civil host.

Once his song has ended, Jarûk offers the characters a quest: destroy the lich Ezzat on level 20 and bring him the lich’s phylactery. The dao promises treasure in exchange and is forced by Halaster’s magic to make good on this promise (see “Treasure” below). If the characters complete Jarûk’s quest and give Ezzat’s phylactery to the dao, the sandy floor turns into a giant vortex that draws Jarûk, the medusas, the sand, and the lich’s phylactery back to the Elemental Plane of Earth. The characters find Jarûk’s promised reward on the floor of the emptied cave. Characters who complete Jarûk’s quest should receive XP as if they had defeated the dao and the medusas in combat.

If the characters destroy Ezzat but give the lich’s phylactery to Ichthyglug the marid in area area 1c, Jarûk knows this and attacks the characters the next time he sees them.

Jarûk can’t leave his cave without Ezzat’s phylactery. If the dao dies here, his body disintegrates into crystalline powder, only to re-form 24 hours later. (The characters don’t receive XP for killing Jarûk more than once.)

The medusas defend the dao to the best of their ability. Jarûk is immune to their Petrifying Gaze.

Treasure

Jarûk wears a pair of golden hoop earrings studded with obsidian (500 gp for the pair) and an amber diadem (7,500 gp). These baubles vanish with the dao when he returns to the Elemental Plane of Earth.

Jarûk’s reward consists of a gem of brightness and two common wondrous items: boots of false tracks and an orb of direction (both described below). These items appear only after the characters complete Jarûk’s quest and help him escape from Undermountain.

The wearer of boots of false tracks can choose to have the boots leave tracks like those of another kind of humanoid of the wearer’s size. Only humanoids can wear these boots.

Someone who holds an orb of direction can use an action to determine which way is north. This property functions only on the Material Plane.

12. Ghaunadaur Shrine

Intelligent Oozes. Clinging to the 20-foot-high ceiling are three intelligent black puddings that were once drow worshipers of Ghaunadaur (see “area Intelligent Black Puddings"). These oozes are hostile toward all intruders. (A battle here also attracts the Huge gray ooze in area area 14.)

Shrine. Nestled in a 12-foot-high alcove at the back of the cave is a misshapen granite altar. Staring out from it is a 1-foot-diameter purple disk inscribed with a black, glaring eye. Looming behind the altar is a 9-foot-tall statue carved in the form of an amorphous, forward-lurching pillar that reaches out with a dozen clawed human arms.

The disk embedded in the altar can be removed by turning it 360 degrees counterclockwise. Removing the disk causes copper coins to spill out from a hollow cavity inside the altar (see “Treasure” below).

If the altar is opened, the multiarmed representation of Ghaunadaur animates and attacks creatures within 10 feet of it or within 5 feet of the altar. The statue is a Large object with AC 17, 50 hit points, a speed of 0 feet, and immunity to acid, poison, and psychic damage. It has the following ability scores: Strength 14, Dexterity 10, Intelligence 3, Wisdom 3, and Charisma 1. It has blindsight out to a range of 10 feet and is blind beyond this radius.

As an action, the animated statue makes a single melee weapon attack (+10 to hit) with its claws. On a hit, the claws deal 22 (5d6 + 5) slashing damage to the target, and any nonmagical armor worn by the target is destroyed.

Treasure

The altar’s hidden cavity contains 2,000 cp.

13. The Scavenger

The Scavenger is a 290-foot-long, 50-foot-wide, 25-ton spelljamming vessel—a ship designed to travel through space. Halaster detected the vessel as it orbited Toril and lured it through a magic gate into Undermountain. He then boarded the vessel, stole its spelljamming helm (the magic device that propels and steers the craft), and took the helm to level 23, leaving the captain and crew to fend for themselves.

Mind flayers constructed the Scavenger to resemble a giant cuttlefish. Its hull is made of an alien resin as hard as thick wood. Behind the ship’s tentacle-shaped rams are two circular windows of transparent crystal resembling eyes, and an upper deck (area area 13a) equipped with four ballistae manned by gray slaadi. An open hatch on the upper deck provides access to the lower deck (area areas 13b through area 13h). The ceilings on the lower deck are 10 feet high.

The ship sits in a 5-foot-deep pool of ooze in an immense cavern, the ceiling of which varies from 30 to 50 feet high. A character can climb the ship’s hull with a successful DC 15 Strength (Athletics) check; the distance from the cavern floor to the upper deck is roughly 20 feet.

The Scavenger is buoyant but has no sails, oars, or other means of propulsion without its spelljamming helm. The vessel can hold up to 10 tons of cargo, and its standard crew complement is twenty. It has AC 15, 400 hit points, a damage threshold of 20, and immunity to poison and psychic damage.

Only a carefully worded wish spell can free the Scavenger from the cavernous depths of Undermountain. Characters who free the ship from its confines can sell it for 20,000 gp, minus 50 gp for each point of damage the ship has taken.

Captain N’ghathrod

The captain of the Scavenger is an illithid pirate named N’ghathrod. N’ghathrod is a mind flayer arcanist (see the sidebar in the “Mind Flayer” entry in the Monster Manual) with 111 hit points. It uses a crystal orb as an arcane focus and dresses in pirate garb. A wooden peg replaces one of its feet, which it lost in battle years ago. Tucked in the pockets of its overcoat are four fist-sized gray gemstones—the control gems for the gray slaadi that guard the ship’s upper deck. N’ghathrod carries a rapier as an affectation but it not proficient with the weapon.

Before it turned to a life of space piracy, N’ghathrod lived in a mind flayer colony on the ringed planet of Glyth, which is farther from the sun than Toril. A few weeks after the Scavenger became trapped in Undermountain, N’ghathrod turned on its orog crew out of hunger, killing four of them and eating their brains. The remaining orog crew members fled to avoid a similar fate. The arrival of adventurers provides N’ghathrod with an unexpected but welcome food source. It tries to separate one party member from the others with a wall of force spell. It then uses its Mind Blast to stun its prey as a prelude to extracting its brain.

If N’ghathrod is reduced to 55 hit points or fewer, its survival instinct supersedes its hunger, prompting it to surrender telepathically. The mind flayer apologizes for its assault and proposes an end to hostilities. Given a chance, it recounts how the Scavenger was orbiting Toril when it was pulled through a magic gate to its current location. It also reveals that the ship’s spelljamming helm vanished shortly thereafter (spirited away by a wish spell, though the mind flayer doesn’t know it). If the mind flayer and the characters establish a truce, N’ghathrod offers to “guard the ship” while the characters set out to retrieve the stolen helm. If the characters succeed, N’ghathrod allows them to claim the vessel as their own, accepting a demotion until it finds a way to get rid of them.

Lair Actions: When fighting aboard the Scavenger, N’ghathrod can take lair actions. On initiative count 20 (losing initiative ties), N’ghathrod can take one lair action to cause one of the following effects:

,- N’ghathrod creates a magical duplicate of itself anywhere aboard the ship. Formed out of psionic energy, this duplicate lasts until it is reduced to 0 hit points, until it is dispelled (DC 15), or until N’ghathrod takes another lair action. The duplicate has the statistics of a normal mind flayer and is friendly toward N’ghathrod, but not under its control. It cannot leave the Scavenger.,- N’ghathrod fills all interior areas of the ship with mind-warping images and sounds of the Far Realm that last until initiative count 20 on the next round. Any creature that isn’t an aberration that starts its turn inside the ship must succeed on a DC 15 Wisdom saving throw or take 10 (3d6) psychic damage.

13a. Upper Deck

Ballistae. Three ballistae are mounted on the forward deck, and a fourth on the aft deck. Four Gray Slaad shapechanged into orogs operate the ballistae, one per weapon.

Hatch. Not visible from the floor of the cavern is an open hatch with a ladder that descends to area area 13b.

A ballista is a Large object with AC 15, 50 hit points, and immunity to poison and psychic damage. Before it can be fired, a ballista must be loaded and aimed. (The ballistae are loaded when the characters first arrive.) It takes one action to load the weapon, one action to aim it, and one action to fire it (+6 to hit, range 120/480 ft., one target). On a hit, a ballista bolt deals 16 (3d10) piercing damage.

Each ballista comes with ten bolts stored in a rack built into the weapon’s stand. A swivel base gives each ballista a firing arc of 180 degrees.

The slaadi have been trained to load, aim, and fire the ballistae. They defend the deck against all boarders, relying on their darkvision to keep watch.

13b. Cargo Hold

Ladder. A ladder bolted to a wall climbs to the upper deck (area area 13a). Hanging upside down on the ladder is a dead orog in plate armor.

Crates. A second dead orog in plate armor, along with its greataxe, lies amid the wreckage of several wooden crates. Toward the back of the hold are five intact wooden crates and five wooden chests secured under heavy cargo nets.

Dead Cook. The hallway leading toward the lower deck’s forward sections contains a third dead orog, this one wearing a bloodstained apron and no armor.

The dead orog on the ladder hangs by one of its spiked boots. A character can use an action to dislodge the dangling fellow. Examination of all three orogs reveals that their skulls were cracked open and their brains sucked out—the hallmark of a mind flayer attack. The orog in the apron lies outside the door to area area 13c.

Treasure

The crew plundered most of the food supplies before fleeing the ship, leaving behind five treasure chests and five intact crates (numbered below for ease of bookkeeping). The chests are unlocked, their locks broken off.

Chest 1 contains 400 sp, 180 gp, and three gold bracelets (25 gp each). Half buried by coins is a 5-inch-diameter miniature beholder made of enameled gold with a black pearl central eye and multicolored spinels at the ends of its eyestalks (2,500 gp).

Chest 2 contains six bolts of elven silk (50 gp each) and an engraved box containing five 3-inch-tall figurines—each one depicting a kind of metallic dragon and made of the appropriate metal (250 gp for the set).

Chest 3 contains six vial of stardust that radiate an aura of illusion magic under the scrutiny of a detect magic spell. An identify spell or similar magic reveals that the dust has a singular magical property. Any creature that sprinkles the dust over itself gains the ability to cast the dream spell once as an action (spell save DC 15), requiring no components.

Chest 4 contains 320 gp and a silk pouch holding four blue pellets, each of which reproduces the magical property of a potion of healing when swallowed.

Chest 5 contains a matching set of five copper goblets with silver filigree (25 gp each), a black coral necklace (250 gp), and a mummified elven hand wearing two gem-studded gold rings (250 gp each).

Crates 1 through 3 contain poisoned rations. A character who inspects these rations and succeeds on a DC 10 Wisdom (Survival) check can tell that they’re unfit to eat. Any creature that ingests a helping of poisoned rations must succeed on a DC 15 Constitution saving throw or be poisoned for 24 hours.

Crate 4 contains 60 days of edible dry rations.

Crate 5 is stamped with the symbol of a smiling gnome face encircled with the words “KRICKENHOF’S KRAFTWERKS” in carnival letters. Packed in peanuts are three gnome inventions: a spring-loaded pogo stick (25 gp), a wind-up tomato masher (125 gp), and a strap-on helmet with a wooden propeller mounted to the top of it. This propeller helm is an uncommon wondrous item to which only a Small humanoid can attune. While worn, the helm allows its wearer to use an action to cast the levitate spell, requiring no components. The helm’s propeller spins and whirs loudly until the spell ends. Each time the spell ends, there is a 50 percent chance that the helm loses its magic and becomes nonmagical.

13c. Galley and Mess Hall

This room contains a dining table, six stools, and a small iron stove. Cupboards built into the walls have been thrown open, their contents (utensils and dishware) scattered across the floor.

Casting a detect magic spell in this cabin reveals an aura of evocation magic emanating from inside the wall that separates this room from area area 13d.

Treasure

Characters who search the cabin and succeed on a DC 20 Wisdom (Perception) spot a tiny hole at the base of the wall that separates this cabin from area area 13d. Two feet above this hole, lodged inside the wall, is a Sending Stones. (The matching stone can be found with the orog first mate in area area 2.)

If a character removes the Sending Stones from the wall, a miniature giant space hamster scuttles out of the hole in the base of the wall and looks rather put out. The space hamster looks remarkably like a normal hamster. It has the statistics of a rat but no attacks (and is worth 0 XP). It has made a nice lair for itself in the walls of the ship but poses no danger if it’s disturbed. A character can befriend the hamster by offering it food.

13d. Captain’s Stateroom

Walls. The resin walls are sculpted and painted to look like glossy black tentacles entwined around one another and the screaming elves in their grasp.

Easel and Paintings. Resting on a wooden easel in the middle of the cabin is a half-finished canvas painting of a colorful alien landscape. Next to the easel, several paintbrushes and jars of paint lie on a small table. Five finished paintings of other alien landscapes are leaning against the back of the easel.

Chair. A bloodstained wooden chair with iron wrist-clamps bolted to its armrests sits in a forward alcove. A pool of sticky blood covers the floor around it.

Secret Compartment. A character who searches the cabin for secret doors and succeeds on a DC 15 Wisdom (Perception) check finds a small hatch built into the floorboards. This hatch conceals a shallow compartment containing Captain N’ghathrod’s spellbook.

N’ghathrod straps captives to this chair before devouring their brains. A creature shackled to the chair can use an action to try to escape, doing so with a successful DC 20 Strength (Athletics) or Dexterity (Acrobatics) check.

Treasure

Before he was transformed into an illithid by the process known as ceremorphosis, Captain N’ghathrod was a spacefaring elf. Although it has no memories of its former life, the mind flayer retains its elven fondness for celestial beauty. The paintings, which illustrate worlds that N’ghathrod has visited, are worth 100 gp each.

N’ghathrod’s spellbook is bound in leather, its contents written in a Braille-like script. The mind flayer uses its tentacles to read the script, which other creatures can decipher with a comprehend languages spell. The book contains all the spells N’ghathrod has prepared, plus animate dead, Bigby’s hand, and Evard’s black tentacles.

13e. Starboard Crew Cabin

This cabin contains two sets of bunks stacked three tiers high.

13f. Port Crew Quarters

This cabin is furnished like area area 13e and also contains a dead orog lying face down on the floor. Examination of the corpse reveals that the orog’s skull was cracked open and its brain sucked out. Lying at the orog’s feet is a greataxe.

13g. Bridge

The door to the bridge stands slightly ajar. N’ghathrod, the mind flayer captain, is here (see the “area Captain N’ghathrod” sidebar). The features of the bridge are as follows:

Windows. Two circular, 9-foot-diameter windows of bulging, transparent crystal rest in bronze fixtures.

Celestial Chart. Painted on the sloped ceiling are familiar constellations and unfamiliar planets.

Grooves. Grooves in the middle of the floor suggest that a piece of furniture once rested there.

Characters who examine the grooves and succeed on an Intelligence (Investigation) check can ascertain that they’re designed to secure a heavy chair or chair-shaped object to the floor. The grooves conform to the footprint of the ship’s spelljamming helm, which can be found on level 23.

The chart on the ceiling has the sun at its center, with elongated rings showing the paths of the eight planets that orbit it: rocky Anadia; Coliar the gas giant; Toril and the small asteroid cluster orbiting it called the Tears of Selûne; the water worlds Karpri and Chandos; the noxious ringed planet Glyth; the asteroid cluster of Garden, which is held together by an enormous plant; and the wheel-shaped H’catha. Beyond the planets are the constellations of Realmspace, all visible in the night skies of Toril at various times of the year.

13h. Oh Captain, My Captain!

The floor here is covered with shattered glass and brine, the remains of jars that once held pickled humanoid brains. The curved walls bear empty shelves where Captain N’ghathrod stored its emergency food reserves. The mind flayer was forced to eat the pickled brains after its crew fled and now hungers for fresh food.

14. Ooze Den

This 10-foot-high cave has become the lair of a Huge gray ooze (see “area Huge Gray Ooze"), which lurks in the northernmost alcove to the right of the entrance. If the characters already fought this ooze in area area 12, the cave is empty.

15. Standing Gate to Level 17

Rising out of a 2-foot-deep pool of ooze is a pair of 15-foot-tall standing stones topped with a lintel, carved into which is a symbol of an arrow. The standing stones form a magic gate (see “area Gates"). Its rules are as follows:

• If an arrow or a crossbow bolt is shot between the standing stones, the gate opens for 1 minute.
• Characters must be 14th level or higher to pass through this gate (see “area Jhesiyra Kestellharp"). The first creature to pass through the gate triggers an elder rune (see “area Elder Runes").
• A creature that passes through the gate appears in area area 8b on level 17, in the closest unoccupied space next to the identical gate located there.

16. Tunnel to Level 20

At the top of the tunnel that descends to level 20 is an 18-foot-high, ring-shaped cavern created by a purple worm that Halaster disposed of long ago.

Aftermath

The characters have a couple of reasons to return to this level after exploring it:

• If they acquire the phylactery of the lich Ezzat, the characters must come back to the Caverns of Ooze with the phylactery to claim their prizes from the marid in area area 1c or the dao in area area 11b. Giving the phylactery to one genie makes an enemy of the other.
• If the characters recover the spelljamming helm that was stolen by Halaster, they can return it to the Scavenger and use a wish spell to expel the vessel from Undermountain.

The level changes little in the characters' absence, at least in the short term. If Ichthyglug or Jarûk is set free, Halaster might trap an efreeti on this level and pit it against whichever genie was denied Ezzat’s phylactery, setting up the new arrival in a cave befitting its fiery nature.