From the Lost City Adventure (actually, the Expert set but this is the only place I have seen it used). Weird monster will use it as a potential encounter in Maze of the Blue Medusae as a cannibal critic “boss”. Original entry:
Thoul. A thoul is a magical combination of a ghoul, a hobgoblin, and a troll (for trolls, see D&D Expert rules). Thouls look like hobgoblins. The party will think these thouls are hobgoblins until they attack. In combat, a character hit by a thoul must save vs. Paralysis or be paralyzed. (This is like a ghoul’s touch, even though thouls are not undead.) A thoul regenerates lost hit points while it is alive. After a thoul is hit, the DM adds 1 to its hit points at the beginning of each combat round. The thouls serve the Priests of Zargon. They hunt for prisoners to take back to the Underground City.
Keen Smell. The thoul has advantage on Wisdom (Perception) checks that rely on smell.
Regeneration. The thoul regains 10 hit points at the start of its turn so long as it has 1 hit point remaining. If the troll takes acid or fire damage, this trait doesn’t function at the start of the thoul’s next turn.
Martial Advantage. Once per turn, the thoul can deal an extra 7 (2d6) damage to a creature it hits with its claw attack if that creature is within 5 feet of an ally of the thoul that isn’t incapacitated.
Multiattack. The troll makes three attacks: one with its bite and two with its claws.
Bite. Melee Weapon Attack: +7 to hit, reach 5 ft., one target. Hit: 7 (1d6 + 4) piercing damage.
Claw. Melee Weapon Attack: +7 to hit, reach 5 ft., one target. Hit: 11 (2d6 + 4) slashing damage. If the target is a creature other than an elf or undead, it must succeed on a DC 16 Constitution saving throw or be paralyzed for 1 minute. The target can repeat the saving throw at the end of each of its turns, ending the effect on itself on a success.