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 is an extremely difficult item to acquire.
- This item cannot be obtained in a world where Skeletron has already been defeated, as Dungeon Guardians will no longer spawn.
- Similar to the Zephyr Fish, the head that follows the player will not teleport to them when they end up a long distance away from it, but rather will just keep moving towards the player. One can instantly teleport it back to themselves by toggling the visibility of it off, then back on again in their pet slot.
- It is most likely designed and named after a 19th century Skeleton key.
- Despite being extremely difficult to acquire, it only sells for