Blood Frenzy. The yuan-ti Malformed has advantage on melee attack rolls against any creature that doesn't have all its hit points.

Limited Amphibiousness. The Yuan-ti Malformed can breathe air and water, but it needs to rest in air fro 5 minute for every 30 minutes spent underwater

 Cold blooded. after being hit with a fire based attack, the yuan-ti Malformed spawns 1 constrictor snake, taking 5 damage

Multiattack. The yuan-ti Malformed can make two attacks with it's claws

Bite. Melee Weapon Attack: +4 to hit, reach 5 ft., one target. Hit: 10 (1d6 + 5) piercing damage and 1d6 poison damage. If this attack hits, the target must make a dc 10 constitution saves or have disadvantage on all attack rolls for the rest of the day

Claws. Melee Weapon Attack: +4 to hit, reach 5 ft., one target. Hit: 10 (2d6 + 5) slashing damage.

Spawn snakes. summoning attack: the yuan-ti infestor rolls 1d20+5 and spawns that many Hp worth of constrictor snakes. If cannot spawn any, next turn 1 spawns.