Shapechanger (2/Short Rest). The abomination can use its bonus action to polymorph into a monstrous beast form, or back into its true form, which is humanoid. Its statistics, other than its AC, are the same in each form. Any equipment it is wearing or carrying isn't transformed. It reverts to its true form if it dies.

Keen Hearing and Smell. The abomination has advantage on Wisdom (Perception) checks that rely on hearing or smell.

Abominable Resilience. When in beast form, the abomination is resistant to bludgeoning, piercing, slashing damage from nonmagical weapons, acid and poison damage.

Multiattack. (Humanoid or Beast Form). The abomination makes two attacks: two with its chain (humanoid form) or one with its bite and one with its claws (beast form).

Bite (Beast Form Only). Melee Weapon Attack: +4 to hit, reach 5 ft., one target. Hit: 6 (1d8 + 2) piercing damage. If the target is a humanoid, it must succeed on a DC 12 Constitution saving throw or be cursed with werewolf lycanthropy.

Claws. (Beast Form Only). Melee Weapon Attack: +4 to hit, reach 5 ft., one creature. Hit: 7 (2d4 + 2) slashing damage.

Spear (Humanoid Form Only). Melee or Ranged Weapon Attack: +4 to hit, reach 5 ft. or range 20/60 ft., one creature. Hit: 5 (1d6 + 2) piercing damage, or 6 (1d8 + 2) piercing damage if used with two hands to make a melee attack.

Beast's Bile (Beast Form Only). The abomination vomits in a 15 foot cone. Every creature in that area must make a DC 12 Dexterity saving throw, taking 14 (4d6) acid damage on a failed save, and half as much on a success.

Slam (Beast Form Only). The abomination slams his head against a creature within 5 feet of it. Both the target and the abomination must make a DC 12 Constitution saving throw or be stunned.