Bone Key

The Bone Key summons a Baby Skeletron Head pet that follows you until you cancel the buff icon, like other pets. It is dropped by Dungeon Guardians. Because Dungeon Guardians have insanely high stats intended to instantly kill most players, this is an extremely difficult item to acquire.

Tips

 * It's likely the player will need some sort of trap mechanism, such as a long hall of spiked ball traps with teleporters on each side, to defeat a Dungeon Guardian and obtain a Bone Key.
 * If you have wings, you can dig a hole in the dungeon deep enough for the guardian to spawn, and then fly up to the surface then encounter it.
 * On the mobile version, using heart arrows and a Hallowed Repeater can stun the Dungeon Guardian completely.
 * Using Minions and Tiki armor can speed up the time required to defeat the Guardian.
 * Work together! If you die, you won't have to restart again, and the other people will help you.
 * Use Gravitation Potions (have at least 5-15), Megasharks (Unreal works best), Vampire Knives, Scourge of the Corruptor, and high defense/Black Belt.
 * Build a 3 block across area until you see the Dungeon rooms and then your way to get the Dungeon Guardian out will be set.
 * Using Frost Armor with range or melee weapons is a good way to deal lots of damage. The frostburn effect works fine against the Dungeon Guardian.
 * Using Turtle Armor and a Black Belt with a bed nearby, all you need to do is dig a hole down into the dungeon where they spawn and just keep falling in over and over and with the Black Belt dodging and Turtle Armor thorn effect eventually you'll get a Bone Key.