Let's make Bats a neutral mob.

It might be interesting to revamp the humble Bat a little. Or, add another kind of Bat called the Vampire Bat, who will randomly attack the player and stick to them, draining health for as long as they're allowed to stay on the player. They're notoriously hard to hit, and won't just attack you. It will attack any passive mob that wanders too close to it's biome, the Dripstone Caves. They won't attack you  or your animals f the area you're in is well lit, however.