Bats are weak flying enemies commonly found in the first area.
Bats spawn clinging to ceilings in the way spiders do, and will begin to fly at you if you move into the parabolic area below them, even if there is no line of sight. Bats will always attempt to fly directly at you, with very little path-finding intelligence.
The main difficulty when dealing with bats is that they tend to approach from above where it can be tricky to hit them, as the arc of the whip is longest at the front, with only minimal range above and behind.
The best course of action when dealing with bats is to run backwards or get to high ground, then wait for the bat to come to you. This will help to level the dangerous height difference and reduce the reliance on your reflexes.
Ideally, you should aim to draw the bat within a 45 degree angle from the ground, so that you can dispatch them by throwing an item upward at them, or at least bring them into the range of your jump-whipping.
Beware trapping yourself in a place where the bat will fly down directly on top of you: It is very difficult to hit enemies directly above you with the whip. It is much more reliable to throw a rope to kill them with the grappling hook, but this is a waste of precious equipment and only a little better than losing a hit point.