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 all 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.
 * If you're using a gun, Chlorophyte Bullets will home in on the guardian to maximize damage.
 * 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 ranged or melee weapons is a good way to deal lots of damage. The frostburn effect works fine against the Dungeon Guardian.
 * Using Fishron Wings, and a Frog Leg players can actually move faster than the Dungeon Guardian when ascending and descending. This means that the player can keep a fight going as long as they need, making the fight very simple.
 * A player using Fishron Wings and a Frog Leg can ascend fast enough for a dungeon guardian to de-spawn quite reliably.
 * Easiest way to kill the Dungeon Guardian is to have 2 players the other one to lure the guardian then if spawned use magic mirror again and again while the player being chased magic mirrors the other one will kill the dungeon guardian.