Huge fiend, chaotic evil

Armor Class: 30

Hit Points: 172(15d12+75) 15d12+75

Speed: 0 ft

STR

20 +5

DEX

1 -5

CON

20 +5

INT

1 -5

WIS

1 -5

CHA

1 -5

Saving Throws: STR +8 1d20+8 , CON +8 1d20+8

Damage Immunities: Bludgeoning, Piercing, and Slashing from nonmagical attacks.

Condition Immunities: Blinded, Charmed, Deafened, Exhaustion, Frightened, Grappled, Invisible, Petrified, Prone, Restrained, Unconscious

Senses: Truesight 1000ft, passive Perception 5

Challenge Rating: 5

Proficiency Bonus: 3

Reactions

Reactive: The Walled One can take one reaction on every turn in combat.
Devour: If a creature roll a critical fail on an attack roll within 10ft of The Walled One, The Walled One as a reaction can attempt to devour it. The creature must pass a DC 12 Dex save. On a success, the creature is dealt 32(5d12) 5d12 acid damage. On a fail, the creature is consumed, automatically dropping to 0hp. If The Walled One is defeated or resummoned before a 3rd death save fail, the creature pops back out in the nearest unnocupied space. If the creature dies inside The Walled One, The Walled One regains all of its HP back.
Impossible to Climb: As a reaction to a creature trying to climb it, The Walled One can use Devour without the critical fail aspect being the trigger.