Giant Bat

Giant Bats are a hostile mob added in the 1.1 update. They can be found once the Wall of Flesh has been defeated in the Underworld. Giant Bats are found in cave systems, much like the normal Bat mob, but have a substantially higher 200 HP. If a Giant Bat is located in deep corruption it has a chance to drop the Soul of Night which is used to craft substantially useful items.  Every so often a giant bat will induce the confused debuff on you, reversing your controls.