Giant Bat

Giant Bat is an enemy that was introduced in the 1.1 patch.

It is a bigger, healthier and stronger version of the Cave Bat. It uses the same bat AI and also spawns in the cavern layer.

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

Triva
Looks like Golbat from the Pokemon series