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

Hellish Form. A creature that touches the devil bat or hits it with a melee attack while within 5 ft. of it takes 5 (1d10) fire damage. In addition, the devil bat can enter a hostile creature's space and stop there. The first time it enters a creature's space on a turn, that creature takes 5 (1d10) fire damage and catches fire; until someone takes an action to douse the fire, the creature takes 5 (1d10) fire damage at the start of each of its turns.

Illumination. The devil bat sheds bright light in a 30-foot radius and dim light in an additional 30 ft..

Water Susceptibility. For every 5 ft. the devil bat moves in water, or for every gallon of water splashed on it, it takes 1 cold damage.

Bite. Melee Weapon Attack: +4 to hit, reach 5 ft., one creature. Hit: 5 (1d6 + 2) piercing damage and 4 (1d6) fire damage.

Flame Wing. The devil bat hurls a fireball at a target that hits everything in a 10 ft sphere. Each creature in that area must make a DC 12 Dexterity saving throw, taking 10 (3d6) fire damage on a failed save, or half as much damage on a successful one. If a target within the sphere is a flammable object that isn't being worn or carried, it also catches fire.