Chameleon Troll

Keen Smell. The chameleon Troll has advantage on Wisdom (Perception) checks that rely on smell.

Regeneration. The chameleon troll regains 10 hit points at the start of its turn. If the chameleon troll takes the damage type that it is currently vulnerable to (see below), this trait doesn't function at the start of the troll's next turn. The chameleon troll dies only if it starts its turn with 0 hit points and doesn't regenerate.

Damage Chameleon. The chameleon troll begins combat by being immune to one type of damage, either 1) fire, 2) cold, 3) thunder, 4) lightning, 5) radiant, 6) necrotic, 7) psychic or 8) force. At the beginning of it's turn what ever type of the above damage did the most damage to it, it becomes immune to, and then roll a 1d8 to determine what damage type would make the regeneration not function. 

Multiattack. The troll makes three attacks: one with its bite and two with its claws.

Bite. Melee Weapon Attack: +8 to hit, reach 5 ft., one target. Hit: 7 (1d6 + 5) piercing damage.

Claw. Melee Weapon Attack: +8 to hit, reach 5 ft., one target. Hit: 11 (2d6 + 5) slashing damage.