Batilisk

Batilisks are flying creatures that live in Caves and come to the surface through unplugged Sinkholes at dusk. They deal a small amount of damage and take 2 hits to kill with a Spear (except with Wolfgang, who takes 1). They drop Batilisk Wings, Monster Meat, Guano, or nothing at all when killed. Additionally, Batilisks periodically drop Guano while moving (much like Beefalo drop Manure).

Like Bunnymen, above-ground Batilisks will sleep if they can't reach their home by morning.

They deal very little damage or none at all to Stone Walls. However, they can fly over them, so don't expect to be able to escape them through a wall barrier.

Hunting
Multiple Batilisks will join together and swarm characters, circling them as the characters move about or stand still. They will let out a cry before breaking their circle to attack a target and will charge straight at their target, allowing for timed attacks or kiting if multiple choose to attack at one time. Batilisks can be killed in one hit from either a Tentacle Spike or Dark Sword.

When facing many Batilisks underground, it is often helpful to bring a Bunnyman along for assistance. Batilisks and Bunnymen are naturally aggressive towards each other. As long as you keep running, Batilisks can't hurt you (much like most mobs), so a safe and efficient way to kill bats is to lure them to the Bunnymen so that you don't even need to pull out a weapon.

Aboveground, if you want to farm Batilisks, stay next to an open sinkhole and hit them as soon as they spawn at dusk. Because of their somewhat predictable attack pattern, target the ones that squeak, so you should be able to kill some without them attacking all at once.

Trivia

 * The name "Batilisk" is a portmanteau of "bat" and "basilisk."
 * Batilisks often engage in battles with Bunnymen and Cave Spiders.
 * In the first pass of Caves (as seen on the livestream), Batilisk spawn rates were high, leading to swarms of (at one point) 40-50.
 * There is a batcave that can be spawned in using the DebugSpawn "batcave".