Bone Chimera

Magic Turtle Shell Resistance. The Bone Chimera has advantage on saving throws against spells and other magical effects.

Undead Resilience. If damage reduces the Bone Chimera to 0 hit points, it must make a Constitution saving throw with a DC of the damage taken - 8 (any damage less than 8 results in a D20 luck check where a 1 is a fail), unless the damage is radiant or from a critical hit. On a success, the  Bone Chimera drops to 1 hit point instead.

Triple Soul. If the Bone Chimera would die it instead loses a head and the attack that would correspond with that head and drops to 40 hit points.

1D6: (1-2) 1st head, (3-4) 2nd head, (5-6) 3rd head.

Multiattack. The chimera makes three attacks: one with its bite, one with its horns, and one with its claws. When its fire breath is available, it can use the breath in place of its bite or horns.

Claws. Melee Weapon Attack: +7 to hit, reach 5 ft., one target. Hit: 11 (2d6 + 4) slashing damage.

(1st head)  Snaping Turtle Bite. Melee Weapon Attack: +8 to hit, reach 5 ft., one target. Hit: 15 (2d8 + 6) piercing damage.

(2nd head) Raccoon Horns. Melee Weapon Attack: +8 to hit, reach 10 ft., one target. Hit: 13 (2d12) bludgeoning damage.

(3rd head) Salamander Acid Breath (Recharge 4–6). The Salamander head exhales fire in a 15-­-foot cone. Each creature in that area must make a DC 15 Dexterity saving throw, taking 36 (8d8) acid damage on a failed save, or half as much damage on a successful one.