Malamar (5e Creature)
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Medium monstrosity, any non-lawful alignment
Contrary. If the malamar or a creature within 10 feet of it would have advantage on an attack roll, ability check, or saving throw, it instead has disadvantage, and vice versa (included in the malamar's stat block).
Suction Cups. The malamar has disadvantage on saving throws to resist being moved.
Multiattack. The malamar makes one attack with its Tentacles and one Night Slash attack. It can substitute either of those attacks with a use of Superpower.
Night Slash. Melee Weapon Attack: +5 to hit, reach 10 ft., one target. Hit: 16 (3d8 + 3) slashing damage.
Tentacles. Melee Weapon Attack: +5 to hit, reach 10 ft., one target. Hit: 10 (2d6 + 3) bludgeoning damage. If the target is a creature, it is grappled (escape DC 16). Until this grapple ends, the malamar can't use its tentacles on another target.
Superpower (Recharge 5-6). Melee Weapon Attack: +5 to hit, reach 5 ft., one target. Hit: 30 (6d8 + 3) bludgeoning damage and the malamar has advantage on all attack rolls it makes until the end of its next turn.
Topsy-Turvy. In response to another creature dealing damage to the malamar, the malamar reduces the damage to 0 and regains 1d6 hit points.