Adaptive killer. When hit by an attack the Vardornid -2 damage off that same weapon if attacked with the same weapon again. It stacks to a maximum of reducing the damage to 2. It works on multiple weapons.

Rampant Killer. You can make two attacks per turn.

Bladed arms. Melee Weapon Attack: +2 to hit, reach 5 ft., 1 target. Hit: 10 (2d8 + 2) [Piercing] damage. 

Claws. Melee Weapon Attack: +3 to hit, reach 5 ft., 1 target. Hit: 8 (2d4 + 2) [bludgeoning] damage. 

Poison breath. Ranged Weapon Attack: +1 to hit, range 5/15 ft., 2 targets. Hit: 6 (1d4 + 2) [poison] damage.

During its turn it can trade a movement action for an extra attack action, changing nothing. 

Murderous Beast. It can react to an attack with its Claws weapon or Poison breath weapon.