The dungeon guardian is a monster that spawns when the player enters the dungeon without killing skeletron. The dungeon guardian has 9999 health and extreme defence, as well as the ability to insta-kill the player upon contact. He always takes 1 damage (2 on critical hit) so the battle will always take long. Upon death he drops the Bone key, an item used to spawn the baby skeletron head.

You can't just simpily walk into the dungeon and expect him to wait for you to walk out. You need to set up an exit before you summon him. If you have a Nightmare Pickaxe/Deathbringer Pickaxe to break the dungeon blocks, you can fly straight up with a gravitation potion.

There are a few things you may need before you start the battle.

Armor: Only take armor that increases your critical hit chance. The defence doesn't matter as he will always one-hit kill you. A black belt will be helpfull as it gives a chance to dodge attack, but be warned, the black belt gives a CHANCE to dodge and can only be obtained in the dungeon during hardmode and after plantera is defeated.

Acessories: It would be good to bring acessories with prefixes that increase your critical hit chance by 4%. It would be great to have a cloud or sandstorm in a bottle with a prefix like this.

Weapons: It is recomended to have a minishark or a gun with a fast fire rate and about 9999 Musket balls. Any prefix that increases critical hit chance would be very good. The guardian is immune to all debuffs, Golden shower won't work.

Potions: You are REQUIRED to have gravitational potions to allow you to fly and keep away from the dungeon guardian. That is if you choose to use potions.

Setup(If you dont want to use potions): You can set up a long pathway and run across it with speed increasing items or swiftness potions. This is not recommended as once you hit the end of the world, you will need a way to get on the other side of the guardian without touching it.

Follow this guide and you should kill the guardian in no time.(Actually in about 14-16 min, but hey better than half an hour).

Please let me know if i should add anything in this guide.