In “Dawn of the Overmind“, below the Undercity of Penumbra, deeper than the Tuennelscape is the Nethermost. This is where the Annulus lies guarded by the Unredeemed Beast. Presented as much as a puzzle than straight up combat my PCs figured out the Annulus was inside the thing and decided to purposely get swallowed and then get it to vomit them up.  This worked but the attack that forced it to vomit them up also killed it.

The lip of a wide basin is before you, its contents hidden in darkness, and silence–a silence that is shattered with a hunting scream so loud that your ears feel as if they were pierced with needles. Rising up in great loops like an uncoiling python, a horrible worm of dragon-like proportions unfolds upward, brushing the ceiling with its 100- foot-long body Purple mucous glistens on the creature’s flanks as it poises above you, and four daunting tentacles, each at least 20 feet long, surround the beast’s eyeless face and circular maw, itself easily large enough to swallow a human whole.

“I am Death. My breath can disperse your fleshy forms like mist, revealing the juicy sweetmeats beneath that I have been so long denied!”

The monster sleeps in the pool of a long dead elder brain within the Nevermost. If combat is triggered off to the side of the battle area, draw four 2-by-2-square areas and label them “maw,” “throat,” “gullet,” and “stomach.”

Players can move their miniatures through these sections and around the other areas of the battle as the fight evolves. Given the creature’s size, an adventurer can occupy one of the worm’s squares; while so doing the PC is either free, grabbed, or swallowed. If it has surprise, the worm emerges with a tentacle attack. It then uses its actions to swallow PCs.

On its next turn, it tries to swallow any character remaining in its maw, then makes another bite attack against a PC it hasn’t grabbed or swallowed. It uses another action point to accomplish this if necessary. Its aim is to swallow all the PCs. If it does, it returns to its pool to digest.

The worm’s flesh becomes dust when it is finally destroyed, leaving behind teeth and a black carapace.

Features of the area
Illumination: dark.
Basin: This pool once held the elder brain before a neothelid consumed it.
Ceiling: The chamber’s ceiling is 150 feet high.
Treasure: In the depths of the basin, the neothelid’s nest is comprised of excess slime mixed in equal portions with illithocyte bodies in various stages of decomposition. Heroes with the stomach, desire, and 10 minutes worth of time to search through this nest discover the following: 37 green data crystals (gems worth 100 gp apiece), 10 blue data crystals (gems worth 200 gp apiece), and 3 red data crystals (gems worth 500 gp apiece). Among the flotsam, the players also discover a psionic amulet that mimics the abilities of an amulet of proof against detection and location, a failing pair of psionic power fists that mimic the abilities of belt of giant strength (note that these gauntlets only fit a hand with three fingers and one thumb. As belt but have PC roll randomly each day), and a bonethriven of mastery (see “Arcana” on page 35), a human skull with removable top, gold plated. The skull is psionically enhanced to preserve any food material placed in it (usually brains). A peaked illithid hood, bright blue coloured. The hood is psionically treated to keep its wearer warm in any natural cold and reduce all damage from cold by 1 per damage die. An illithid hand knife: delicate, silvery, and deadly. Though smaller than a dagger, it is psionically enhanced such that it acts as a weapon +3, doing damage as a longsword despite its small size. In combat, it can be wielded as if it were a dagger for proficiency bonus. A Human mask. Made of real human skin, this mask appears horrifying when not in use, but when placed over a face (even an illithid face), the mask is psionically energized to animate, mimicking a human face so well as to be 90% undetectable as the real thing (”Look, I’m a human!”).  Another distinctly illithid peaked hood, also bright red coloured; however, this hood keeps its wearer cool in warm conditions, and reduces all damage from fire by 1 hp per damage die.

A crystal fob. Within the 1-inch-diameter crystal, an eye floats, blinking now and then. Whoever holds the eye gains the ability to see simultaneously in both the visible and the infrared spectrum to their normal ranges and a ring of Ilsensine.

The true treasure is the Annulus which lies in the creature’s gullet. It can be retrieved by entering the gullet or killing the Unredeemed Beast.

Gargantuan aberration (mythic), lawful evil
Armor Class 19 (natural armor)
Hit Points 1148 (41d20 + 328)
Speed 50 ft.

29 (+9) 6 (-2) 26 (+8) 18 (+4) 16 (+3) 12 (+1)

Saving Throws Int +9, Wis +8, Cha +6
Senses blindsight 120 ft., passive perception 13
Languages telepathy 120 ft.
Challenge 23 (50,000 XP)

Glutton (1/Day). The fundamental neothelid makes one tentacle attack as a free action at any time but cannot interrupt another creature mid-turn.

Keening. All creatures that start their turn within 25 feet of the take 15 psychic damage. Creatures inside the neothelid are not affected by this aura.

Legendary Resistance (3/Day). If the fundamental neothelid fails a saving throw, it can choose to succeed instead.

Magic Resistance. The fundamental neothelid has advantage on saving throws against spells and other magical effects.

Psi Detector. The fundamental neothelid is aware of the presence of psionic creatures within 1 mile of it and any use of psionic items. It knows the distance and direction to each creature or item, as well as each creature’s Intelligence score, but can’t sense anything else about it. A creature protected by a mind blank spell, a nondetection spell, or similar magic can’t be perceived in this manner. This also protects the creatures psionic items.

Sections. The fundamental neothelid is so big it is its own lair and is split into sections. Inside of each section of the neothelid —maw, throat, gullet, and stomach— is 10-by-10 feet and dark. A creature inside the worm but not swallowed has advantage against the worm. Moving from a section deeper in the worm to a section closer to the maw requires a move action and an Escape DC 24 check. Moving deeper into the worm requires only a move action.

Multiattack. The fundamental neothelid makes one tentacle attack, two crush attacks, and uses nuclear slag if available.

Tentacles. Melee Weapon Attack: +16 to hit, reach 15 ft., one target.
Hit: 22 (2d12 + 9) bludgeoning damage plus 13 (3d8) psychic damage and 1 random psionic affect triggers if it fails to swallow a creature (spell save DC 16):

  1. levitate (no limit)
  2. confusion (1/day)
  3. feeblemind (1/day)
  4. telekinesis (1/day)

If the target is a Huge or smaller creature, it must succeed on a DC 24 Strength saving throw or be swallowed by the neothelid. See lair actions for what happens.

Crush. Melee Weapon Attack: +16 to hit, reach 10 ft., one target.
Hit: 20 (2d10 + 9) bludgeoning damage. A target creature is also grappled and restrained (escape DC 19) until the neothelid moves. The neothelid can grapple up to two creatures at once; at least one of the neothelid’s crush attacks must be directed against each creature it has grappled. All creatures inside the neothelid are also attacked (DC 26 Dexterity saving throw to halve the damage).

Nuclear Slag (Recharge 5–6). The fundamental neothelid vomits radioactive poison in a 90-foot line that is 10 feet wide. Each creature in that area must make a DC 22 Dexterity saving throw, taking 67 (15d8) radiation damage on a failed save and gain a level of exhaustion, or half as much damage on a successful one and not be exhausted. This attack strips away poison resistance by one step for the rest of the encounter each time it damages a target – eventually making the target vulnerable. This occurs before applying damage. This damage has no effect on brain matter. A creature that rolls a natural 1 on the saving throw is mutated. A creature reduced to 0 hit points is dead and turns to ash leaving only its brain and a morbid shadow burned into the floor or wall where it died.

If a creature is inside the neothelid when it uses its nuclear slag action each creature takes maximum damage and have disdvantage on the saving throw.

Do you want to be Devoured? The fundamental neothelid makes one tentacle attack.

The fundamental neothelid can take 3 legendary actions, choosing from the options below. Only one legendary action option can be used at a time and only at the end of another creature’s turn. The neothelid regains spent legendary actions at the start of its turn.

  • Mental Shriek. All creatures with an intelligence score 4 or higher within 120 feet of the neothelid must succeed on a DC 19 Wisdom saving throw or be frightened for 1 minute. A frightened creature repeats the saving throw at the end of each of its turns, ending the effect on itself on a success. Creatures protected from telepathic contact are immune to this attack.
  • Death Roll (2 actions). The fundamental neothelid moves half its speed and begins thrashing about making a Crush attack against all creatures in reach. Any structures or objects in spaces the neothelid moves through take double Crush damage automatically.
  • Devour (2 actions). The fundamental neothelid makes one tentacle attack.

On initiative count 20 (losing initiative ties), the fundamental neothelid automatically takes all its lair actions. These only affect creatures in that section of the worm. If the neothelid takes 50 damage or more on a single turn from a creature inside it, the neothelid must succeed on a DC 20 Constitution saving throw at the end of that turn or regurgitate that swallowed creature and all creatures further up the gullet, which fall prone in a space within 10 feet of the neothelid. If the neothelid dies, a swallowed creature is no longer restrained by it and can escape from the corpse by using 20 feet of movement, exiting prone.

  • Maw. Creatures in the maw must make a DC 28 Dexterity saving throw or take 10 (1d12 + 4) acid damage, and the target is swallowed. The target is forced into the throat.
  • Throat. Creatures in the maw must make a DC 28 Dexterity saving throw or take 10 (1d12 + 4) acid damage, and the target is swallowed. The target is forced into the gullet.
  • Gullet. Creatures in the maw must make a DC 28 Constitution saving throw or take 10 (1d12 + 4) acid damage, and the target is swallowed. The target is forced into the stomach. The Annulus can be found here.
  • A swallowed creature is blinded and restrained, it has total cover against attacks and other effects outside the neothelid, and it takes 35 (10d6) acid damage at the start of its turn.

When the Annulus is approached it will shock the target for 3 (1d6) lightning damage and push the target back. It takes 3 successful Wisdom saving throws to push through the psionic protection and each pass or fail doubles the damage taken. The PC can try for as long as they wish.