Bat

Bats are hostile/neutral mobs. They spawn at night or in dark caves underground. They move around by flapping their wings and bouncing around. They periodically turn red, and when they do, they will inflict damage upon contact. Bats are unique in that they do not specifically target you until they have taken damage. When a bat isn't at full health, it will target a player and swarm them. When attacked they will bounce high in the air. Since they mostly spawn in caves, fighting bats may be hard because caves are dark all around and they can easily pounce on you when you least expect it. Try to note the timing between their normal and hostile states so that you can block their attack, counter-attack, then repeat at the right moments to minimize damage. Bats drop Bat Wings upon death, and like other hostile mobs their health and drops depend on the size of the bat.

Quick Recap:
 * Bats spawn at night and underground in dark areas.
 * Bats do NOT purposely attack players when they have full health.
 * When bats turn red, they become hostile and will inflict damage on contact.
 * The bigger the bat, the more health it has and the more gold and Bat Wings it will drop on death.

Notes:
 * Oddly, bats may drop multiple Bat Wings, especially the bigger ones, even though they only have two.
 * Since bats bounce around, it may be hard to get a good hit on them with a melee weapon. Try a ranged weapon!
 * If a bat is killed by lava, they will NOT drop anything.
 * Bats can regenerate health.

Trivia:
 * In the older versions of the game, bats actually flew around rather than bouncing everywhere, and caused contact damage every time.
 * Bats may fly up and "hug" corners of caves.
 * If a bat regenerates back to full health, it will stop trying to kill you. They won't try not to, though!