Chestburster

Acid Splash. When the Chestburster takes Bludgeoning, Piercing, or Slashing damage, any creature within 5 feet of the Chestburster must make a DC 14 Dexterity saving throw. On a failed save, the creature takes 2d8 Acid damage and must make a DC 16 Constitution saving throw at the start of their next turn.  Every saving throw after the initial save cut the damage dice in half. Once the dice cannot be divided any further the creature no longer needs to make saves. Succeeding on any save negates the need to make future saves from the splash.

Kane's Son. While the Chestburster is gestating, it has total cover from all attacks and spells. The Chestburster uses its Emerge action 1d4 hours after the host wakes up from implantation.

Bite. Melee Attack: +3 to hit, reach 5 ft. Hit: # 1d12 + 1 piercing damage.

Emerge. The Chestburster may only use this action while inside of its host. The Host must make a DC 14 Constitution saving throw. Failure. The Host is immediately killed as the Chestburster forces its way out of the host's chest. Success, the host takes 2d6 Bludgeoning damage.If this damage would reduce the host to 0 HP then treat the save as a failure  Regardless of the result, initiative is rolled immediately. If the save is failed immediately, the party is Surprised. If the save is a success, then the Chestburster repeats this action on each of its turns until it is born.