Buchembrallor

Amphibious. Buchembrallor can breathe air and water.

Legendary Resistance (3/Day, or 5/Day in Lair). If Buchembrallor fails a saving throw, he can choose to succeed instead.

Multiattack. Buchembrallor makes three Claw attacks. He can replace one attack with a use of Spellcasting to cast Mind Spike (level 5 version).

Claw. Melee Attack Roll: +15, reach 15 ft. Hit: 17 (2d8 + 8) Slashing damage plus 10 (3d6) Poison damage.

Poison Breath (Recharge 5–6). Constitution Saving Throw: DC 20, each creature in a 90-foot Cone. Failure: 70 (20d6) Poison damage. Success: Half damage.

Spellcasting. Buchembrallor casts one of the following spells, requiring no Material components and using Charisma as the spellcasting ability (spell save DC 19):

At Will (at 5th spell level): Detect Magic, Mind Spike, Ray of Sickness
2/Day Each: Geas, Modify Memory, True Polymorph

Legendary Action Uses: 3 (4 in Lair). Immediately after another creature’s turn, Buchembrallor can expend a use to take one of the following actions. He regains all expended uses at the start of each of his turns.

Sickening Spit. , Buchembrallor uses Spellcasting to cast Ray of Sickness (level 5 version).

Noxious Burst. Constitution Saving Throw: DC 20, each creature in a 30-foot-radius Sphere centered on a point Buchembrallor can see within 90 feet. Failure: 17 (5d6) Poison damage, and the target takes a −2 penalty to AC until the end of its next turn. Failure or Success: Buchembrallor can’t take this action again until the start of his next turn.

Retribution. Buchembrallor moves up to half his Speed, and it makes one Claw attack.