Limited Telepathy. The abomination can magically transmit simple messages and images to any creature within 120 feet of it that can understand a language. This form of telepathy doesn't allow the receiving creature to telepathically respond.

Limited Shapeshifting. The abomination can magically transform into a creature of any appearance for the duration of one hour, they retain all of the stats and transform into their true form upon being discovered. This transformation isn't completely believable and has some noticeable differences from what it should look like. If a creature has a passive perception of 18 or higher than they discover it is a shapeshift. Otherwise have the creature do a DC 15 perception check to determine if they figure it out.

Multiattack. The abomination makes five attacks: one with its bite, one with its claw and three with its tentacles.

Bite. Melee Weapon Attack: +8 to hit, reach 5 ft., one target. Hit: 25 (4d12 + 5) piercing damage. If the target is a creature, it must succeed on a DC 15 Constitution saving throw against disease or become poisoned until the disease is cured. Every 24 hours that elapse, the target must repeat the saving throw, reducing its hit point maximum by 6 (1d12) on a failure. The disease is cured on a success. The target dies if the disease reduces its hit point maximum to 0. This reduction to the target's hit point maximum lasts until the disease is cured.

Claw. Melee Weapon Attack: +8 to hit, reach 15 ft., one target. Hit: 11 (2d6 + 5) piercing damage. If the target is a creature, it must succeed on a DC 10 Dexterity saving throw against being knocked prone.

Tentacle. Melee Weapon Attack: +8 to hit, reach 15 ft., one target. Hit: 8 (2d4 + 5) bludgeoning damage plus 12 (4d6) piercing damage. If the target is Medium or smaller, it is grappled (escape DC 15) and restrained until the grapple ends. The abomination has three tentacles, each of which can grapple one target.

Tentacle Slam. The abomination slams creatures grappled by it into each other or a solid surface. Each creature must succeed on a DC 15 Constitution saving throw or take 18 (4d6 + 5) bludgeoning damage and be stunned until the end of the abomination's next turn. On a successful save, the target takes half the bludgeoning damage and isn't stunned.

Frightful Presence. Each creature of the abomination's choice within range must make a DC 15 Wisdom saving throw or be frightened for 1 minute.