Echolocation. The bat can't use its blindsight while deafened
Keen Hearing. The Vampire Bat has advantage on Wisdome (Perception) checks that rely on hearing
Bite Melee Weapon Attack: +2 to hit, reach 5ft, one creature. Hit: 1d4 Piercing Damage. If the creature hit has blood, the Vampire Bat regains half the damage dealt, rounding up.