Illuminant Bat

The Illuminant Bat is a hallowed version of the Giant Bat, and is slightly stronger. It only spawns in the underground Hallow (cavern layer under the hallow biome). Just like its name suggests, the Illuminant Bat emits a little amount of light.

Like many mobs introduced in 1.1, the Illuminant Bat will only spawn after the Wall of Flesh has been defeated.