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Image promptgargantuan aberrant maw-and-tendril horror, vast toothed gullet, dozens of grasping tendrils, glistening dark hide, dripping steaming acid, rising from crumbling dungeon oubliette pit, swelling engorged bulk, dragging prey inward, blind sensing menace, bruised black-purple hide, bile-yellow acid, crimson inner maw, sickly underglow, dark fantasy, grimdark, painterly digital art, dramatic chiaroscuro lighting, muted desaturated palette with corrupted-crimson accents, weathered post-Cataclysm atmosphere, intricate high detail, cinematic composition

Oubliette Horror

Gargantuan Aberration, Chaotic Evil
CR 20BruteDungeon / Structure
AC 20
HP 375 (25d20 + 125)
Speed 40 ft., Climb 40 ft.
STR
28
+9
save +15
DEX
12
+1
save +1
CON
21
+5
save +11
INT
8
−1
save −1
WIS
16
+3
save +9
CHA
10
+0
save +0
Resistances Cold, Fire, Lightning; Bludgeoning, Piercing, Slashing (nonmagical)
Immunities Poison; Blinded, Charmed, Frightened, Poisoned, Prone
Senses Blindsight 120 ft.; Passive Perception 19
Languages —

Traits

Legendary Resistance (3/Day).

Siege Monster. Double damage to objects.

Devouring Growth. When the Oubliette Horror swallows a creature, it gains 25 temporary Hit Points and its Speed increases by 10 feet (until the end of combat, up to a maximum of +30).

Actions

Multiattack. Makes one Maw and four Tendril attacks.

Maw. Melee Attack Roll: +15, reach 15 ft. Hit: 38 (6d8 + 11) Piercing damage. If the target is Large or smaller, it makes a DC 23 Strength save. Failure: The target is swallowed — it has the Blinded and Restrained conditions, has Total Cover against outside attacks, and takes 28 (8d6) Acid damage at the start of the Oubliette Horror's turn. Escape: an action plus a DC 23 Strength (Athletics) check. It can have three creatures swallowed at once.

Tendril. Melee Attack Roll: +15, reach 20 ft. Hit: 22 (3d8 + 9) Bludgeoning damage, and the target makes a DC 23 Strength save. Failure: Grappled (escape DC 23) and pulled 20 feet.

Consume (Recharge 6). The Oubliette Horror expands its body. Every enemy in a 30-foot Emanation makes a DC 22 Dexterity save.

  • Failure: 66 (12d10) Acid damage, and the target has the Grappled condition (escape DC 23).
  • Success: Half damage.

Legendary Actions (3/Round)

Tendril Lash. Makes one Tendril attack.

Digest (Costs 2). Every swallowed creature takes 28 (8d6) extra Acid damage.

Shift Mass (Costs 2). Moves half its Speed; this movement doesn't provoke Opportunity Attacks.

How to Use

The thing at the bottom of the dungeon. A pure Brute — 375 HP, ~130 damage per round.

Devouring Growth is critical: everyone it swallows strengthens it. The longer the fight drags on, the faster and tougher the Oubliette Horror becomes.

Key

Speed. End this fight fast. Rescue swallowed allies immediately (or Digest kills them). Freedom of Movement cancels Grappled — critical.