Stirge

Blood Drain. _Melee Weapon Attack:_ +4 to hit, reach 5 ft., one creature. _Hit:_ 4 (1d4+2) piercing damage, and the stirge attaches to the target. While attached, the stirge can't attack, and at the start of each of the stirge's turns, the target loses 4 (1d4+2) HP due to blood loss. The attached stirge moves with the target whenever the target moves, requiring none of the stirge's movement. If can detach itself by spending 5 feet of its movement on its turn. It does so after it drains 8 HP of blood from the target or the target dies. A creature, including the target, can use its action to detach the stirge.

Reactive Wiggle. When the stirge is the target of an attack from a creature within 5 feet of it while it is attached to a creature, the stirge can wiggle, exposing the flesh where it is attached. The attacker must succeed on a DC 12 DEX save or the attack targets the creature to which the stirge is attached instead of the stirge.