The Tarnished Crown is an Item used to unlock the Shipwrecked character, Wilbur. It has a 10% chance to drop when any Prime Ape dies or any Prime Ape Hut is destroyed. The drop will not be available if Wilbur is already unlocked or a Tarnished Crown already exists in the world.
If Wilbur is not unlocked yet, the Soggy Monkey can be found on a Raft in the Shallow Ocean. Giving the Soggy Monkey the Tarnished Crown will unlock Wilbur. The spawn code for the Soggy Monkey is "wilbur_unlock".