Bone Key

The Bone Key is a pet-summoning item that is always dropped from the Dungeon Guardian. Upon use, it summons a Baby Skeletron Head pet which follows the player around infinitely. The Baby Skeletron Head floats around the player and sometimes spins its head, much similarly to Skeletron's spinning head attack or the Dungeon Guardians in general. This action may also occur if the player is a bit further away from the Skeletron Head. Because Dungeon Guardians have extremely high stats intended to instantly kill all players, this can be a difficult item to acquire.

Trivia

 * It is most likely designed and named after a 19th century, known erroneously and commonly as a skeleton key.
 * Despite being extremely difficult to acquire, it only sells for.