Agate

Not to be confused with the item of the same name

Agate is a doll of agate stone that stays dormant and motionless when first found. It wakes on its own after a random 10 to 60 seconds, or at once if attacked. Once awake it chases the player and lunges into a close melee slash at about three blocks' reach. Its movement is erratic, which makes it easy to keep circling and hitting on the move.