Aril Eldish, the Grand Butcher (Forgotten Beast, Dwarf Fortress)

Bladed Slimy Armor, Acidic Aura. Aril Eldish is surrounded by a thick armor made of protective ooze, giving it the following benefits for as long as it remains:
- Its size category is Huge
- Its Armor Class increases by 4 (included in its AC)
- It has advantage against saving throws made against spells except those that deal cold damage
- Its Pseudopod/Claw and Bite attacks also deal an additional 3d8 slashing damage on a successful hit
- Creatures, as well as objects not being worn or carried within 15ft of Aril Eldish must make a Constitution Saving Throw at the beginning of their turns, taking 11 (2d10) acid damage on a failed save, or half that damage on a success.
- Its melee weapon attacks gain 10 ft. of range.
- Aril Eldish loses its Bludgeoning damage vulnerability
- Aril Eldish can climb difficult surfaces, including on walls and upside down on ceilings, without needing to make an ability check.

Once Aril Eldish has 50 or fewer Hit Points remaining, the armor dissipates, removing these benefits. The armor regenerates after Aril Eldish completes a Long Rest.

Multiple Heads. Aril Eldish has two heads, both with and without its Slimy Armor. While it has more than one head, it has advantage on Saving Throws against being blinded, deafened, frightened, stunned, and knocked unconscious. Whenever Aril Eldish takes 25 or more damage in a single turn, one of its heads dies. If both of its real heads die, Aril Eldish dies. If both of its Slimy Armor heads die, it becomes blinded and deafened until it can regrow one of its slimy heads. It regrows one slimy head at the end of its turns, up to two, unless it has taken cold damage since its last turn.

Reactive Heads. If Aril Eldish has both heads from Slimy Armor, it gets an extra reaction per turn that it can use for opportunity attacks.

Compound Eyes. Aril Eldish has advantage on initiative rolls, opportunity attacks, and ability checks that rely on sight.

Spellcasting. Aril Eldish is a 10th-level spellcaster. Its spellcasting ability is Charisma (spell save DC 16, +6 to hit with spell attacks). Aril Eldish has following spells prepared:
Cantrips (at will): Acid Splash
1st level (4 slots): Chromatic Orb, Chaos Bolt
2nd level (3 slots): Acid Arrow
3rd level  (3 slots): Glyph of Warding
4th level (3 slots): Elemental Bane, Vitriolic Bolt
5th level (2 slots): Telekinesis

Pseudopod/Claw. Melee Weapon Attack: +8 to hit, reach 15/5 ft., 1 target. Hit: 15 (2d8 + 6) bludgeoning (plus 19 (3d8 + 6) slashing if Bladed Slimy Armor is in effect) damage.

Bite. Melee Weapon Attack: + 8 to hit, reach 15/5 ft., 1 target. Hit:  (1d8 + 6) piercing (plus 19 (3d8 + 6) slashing if Bladed Slimy Armor is in effect) damage.

Multiattack. Aril Eldish makes two Pseudopod/Claw attacks and one Bite attack.

Cast a spell. Aril Eldish casts a spell from its spell list.

Opportunity Attack. If a creature moves outside of Aril Eldish's attack range, it can use its reaction to make a Pseudopod or Bite attack against that creature.