Bat

The Bat is a mob that can spawn only in dungeons and the Roofed Forest Island with a Roofed Forest Crystal on it.

They spawn in a range of 1 block away and 3 block in high to the crystal. The spawn area must be unblocked.

A bat spawns every 43 seconds until five are on the island. Spawning continues as long as this cap is not reached.

Drops
When killed by the player, the bat drops and a high amount of XP. It also has a small chance of dropping the Bat Talisman Accessory. When in dungeons it can drop multiple items or a blessing and is counted as a secret when killed.

In Dungeons
Bats can spawn in Dungeons. They count as a Secret when killed and can drop various dungeon items or a Blessing.

Trivia

 * The Bat Talisman drop is pretty hard to find, having a 1.84% drop chance, or about 3/163 (1/54).
 * They spawn only on the Roofed Forest Island at night. They also rarely spawn in dungeons in the Catacombs level.
 * A trapping system can lure bats to one specific spot for easier killing.
 * A Night Saver enables constant bat spawning.
 * An AFK pool and a cleave weapon can be a no-redstone alternative to a redstone-powered system.
 * Bats can be AFK'd and will still drop talisman when drowned. AFK design
 * if Bat secrets die by non-player means(i.e. fire or mob attacks such as Crypt Dreadlord skulls) they won't count as a secret found.
 * The Hurricane Bow with its ability maxed helps a lot with hitting the bats as they are very small and fast.