Killer Bunny

The Killer Bunny is a variant of a Rabbit, but it is hostile towards all players, wolves, and foxes. Its fur is completely white and its eyes are red and horizontal, unlike regular rabbits. This mob will never spawn naturally and there are no specific methods to spawn them other than commands.

A Killer Bunny (via screenshot)

Spawning

The Killer Bunny can only be spawned with the " /summonrabbit ~ ~ ~ {RabbitType:99}" command. Once spawned, it will have a nameplate over its head which will read “The Killer Bunny”. If the game is set to peaceful difficulty, the Killer Bunny will not attack players, but it will attack wolves and even tamed dogs. The Killer Bunny can be actually bred and have a chance of the offspring being another Killer Bunny.

Attack

After a Killer Bunny is spawned, it will look for players and attack them when within a 16-block radius. Once it has decided to attack, it will quickly start hopping toward the player to attack them. Once close enough to the player, it will lunge at them and deal quite a bit of damage.

A Killer Bunny killing a wolf (via screenshot)

Conclusion

Since Killer Bunnies cannot spawn naturally, they aren't a real threat but if you have decided to spawn them in with commands, it is highly recommended that you use a sword made of Iron or better to fight them.