He's Right Behind Me

A rare mob will spawn by the name of Percival that will quietly appear behind you and attack when you least expect it.

The simple way of getting rid of him is by hitting him a few times when you see him before he attacks. He despawns after 30 seconds when he initially spawns.

Percival has a relative named Howard. Howard only attacks while not being looked at and is immune to player-based damage. Can be killed by other mobs and fire.

There are also some unstable experimental features that should not be messed around with if players intend to keep their world.

Enjoy :)