Echolocation. The bat can't use its blindsight while deafened.

Keen Hearing. The bat has advantage on Wisdom (Perception) checks that rely on hearing.

Bite. Melee Weapon Attack: +5 to hit, reach 5 ft., one creature. Hit: 1d4 + 3 piercing damage.

Screech. 

Once per dusk the Abyssal Bat can target all creatures within a 20ft range of itself and sunder their minds with it's Screech. Each creature within range must make a Con saving throw (DC 14) or be temporary paralysed until the end of it's next turn. Each creature also takes 4d4 psychic damage on a failure, half as much on a success. 

Leech. As a bonus action you can activate Leech when you make a Bite attack. 

Melee Weapon Attack: +5 to hit, reach 5 ft., one creature. Hit: 2d4 + 3 piercing damage. The Abyssal Bat regains Hit points equal to damage dealt.