Guide:Dungeon Guardian strategies

The Dungeon Guardian is the strongest monster in Terraria and spawns when you try to enter the dungeon before defeating Skeletron, or when failing to defeat Skeletron before dawn. There is little reason to fight him, except for the Bone Key he drops. A good way to beat him is have muiltiple players build a house on top of the dungeon, place a bed and set your spawn point, and then have someone go in the dungeon and get the Guardian. The reason you need muiltiple players is so someone can always be alive so he doesn't despawn.

Terrain Preparation
As he will instantly kill you when he touches you the only way to defeat him is to outrun him. Therefore you have two good options for terrain. First is simply use the whole map, by using Gravitation Potions to move around. You will fall faster than him and you can move diagonally to go even faster. The second option is a very long (single-layer) Skybridge. You will be equally fast as the Dungeon Guardian when running horizontally. If you want to outrun him make a diagonal skybridge (any blocks except platforms work for this) or build the skybridge out of Asphalt.

To "summon" the Dungeon Guardian, it is recommended to dig a straight shaft down from outside the dungeon. The Depth Meter is recommended for this.

If the player has access to the Mechanic and Steampunker it is possible to build a Teleporter arena (example). This can make the fight dramatically easier, especially if the Teleporters are automated with Timers. As the Mechanic is found in the Dungeon it is however likely that this requires the player to bring materials from a world where Skeletron has already been defeated.

Last of all, you need to be in a world where Skeletron has NOT been defeated.

Notes:
The Dungeon Guardian travels faster than running speed if Frostspark boots are used.

It is advised that players use an asphalt skybridge.

Gearing Up
As the Dungeon Guardian will instantly kill you, your defense is entirely irrelevant (unless using the maximum defense available; more on this tactic below). For this reason, it is recommended that you use mobility accessories rather than defensive ones. Also, because its defense is so high that damage doesn't matter, there are only a few items which are actually useful.The turtle armor deals a thorns efect that could kill the dungeon guardian if you already hit him some times.

Armor
If available use Frost armor, as the Dungeon Guardian is not immune against the Frostburn debuff, greatly increasing the damage. It also provides a good critical bonus. Another option would be Chlorophyte armor, as a full set summons a leaf that also shoots at the Dungeon Guardian and it also provides a crit bonus. Same goes for the set bonus of Orichalcum armor. Yet another option is to use Beetle armor with the shell along with defensive accessories and an Endurance Potion and Lifeforce Potion to give you a fairly good chance of surviving a hit from the Dungeon Guardian should it happen to hit you. You can also use Tiki Armor if you want to use minions. Another good armor to use would be Titanium armor as once you use any attack it makes you invincible to damage.

Weapons
Ranged weapons are the only viable type of weapon for this fight. Furthermore the weapon should have a high firing speed. Recommended is any prefix that increases critical hit chance or firing speed.
 * Some high firing ranged weapons are Chain Gun, Gatligator, Megashark, Minishark and Uzi. Combine them with Crystal Bullet for additional damage from the released fragments, or Chlorophyte Bullets and a Chain Gun to deal damage at an insane rate.
 * Bows that may be useful are the Tsunami or Pulse Bow, due to them firing multiple projectiles. Combine them with Holy Arrows for more damage (which is mainly useful if you do not make use of the skybridge method).
 * The Piranha Gun is a very easy to use ranged, 'homing weapon', that deals significant damage.
 * Useful magic weapons would be Razorpine, Crystal Storm, Leaf Blower, Bubble Gun and, if you use the skybridge method, Blizzard Staff.
 * If you want to use melee damage based weapons using Vampire Knives, the Scourge of the Corruptor, the Mushroom Spear, the Possessed Hatchet, or the Flairon are possibilities.
 * Although most minions are useless, due to them being too slow. The Optic Staff and Tempest Staff can be helpful, due to their minions shooting projectiles.
 * If you are playing with friends, take the Dungeon Guardian to spawn and fly in circles while attacking with Vampire Knives and let your friends use the Scourge of the Corruptor and blast tiny eaters at it.
 * If using Minions you can use the Optic Staff or Tempest Staff to do lots of damage while the player concentrates on dodging.
 * Any bow that is higher than silver or tungsten bow and Heart Arrow.

Accessories
Prefixes for accessories should be more critical hit chance or more movement speed.
 * Try to use Gravitation Potions, Spectre Boots as well as a Shiny Red Balloon, or any upgraded version of those items. These will be needed when you reach the end of the skybridge to jump over the Dungeon Guardian when switching direction. Furthermore you need to be able to run and reach the   horizontal speed cap.
 * If you do use Gravitation Potion an item to negate fall damage or provide running may still be useful.
 * If you use any type of wings, the Frog Leg is very useful because it provides 50% increased flight speed and range. The best wings to use are the Fishron Wings and the Hoverboard for their increased vertical and horizontal movement speed, respectively.
 * Black Belt or Master Ninja Gear give you a chance to dodge an attack. This is especially useful in combination with Turtle armor and Cross Necklace.
 * Destroyer Emblem and Eye of the Golem for their increased critical chance.
 * A Mana Flower, in case you use magic weapons.
 * Optionally a Depth Meter/GPS, so you can see when you move past the 0 depth line, causing the Dungeon Guardian to spawn.
 * With Minions you can use Pygmy Necklace, Necromantic Scroll, and a Papyrus Scarab.
 * If you use a skybridge, a Cobalt Shield, Obsidian Shield, or Ankh Shield will prevent enemies from knocking you into the Dungeon Guardian.

Potions

 * Gravitation Potions, in case you use that method.
 * Swiftness Potions and something to give you the Well Fed buff, to increase your movement speed.
 * Any Mana Potions if you use magic weapons.
 * Optionally some Rage Potions and potions that provide light, such as Hunter, Night Owl and Shine Potions.
 * A Summoning Potion can be used to allow the usage of an extra minion.
 * An Ammo Reservation Potion is great for bullet damage.

Teleporter Method
X=Teleporter

"=Pressure Plate

-=Wire

%=Hole to dungeon

"""      """  XXX---XXX %%%      %%%

After making the setup, lure a Dungeon Guardian between the Teleporters, and step on the pressure plate. You will rapidly teleport back and forth, and the Dungeon Guardian will stay between the Teleporters. Keep hitting the Dungeon Guardian until it is dead.

Alternatively, if you decide to kill the Dungeon Guardian after the Moon Lord, you can use a Portal Gun in a similar fashion. Just make sure the portals are far enough away from each other and that you don't jump into the portal from a high distance, as you will keep the momentum when you get out at the other portal. This could make it so that you don't teleport back and forth fast enough since it takes longer to drop back into the portal once you jump out.

Easy Kite Method
With 1.3 you can use the Cosmic Car Key and by flying around the world you will be moving faster than the Dungeon Guardian using summons or a ranged weapon to make the fight very simple (example).

General tips

 * 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.
 * On the mobile version, using heart arrows and a Hallowed Repeater can stun the Dungeon Guardian completely.
 * Using Minions and Tiki armor can shorten the time required to defeat the Guardian.
 * Work together! If you die, you won't have to restart again, and with multiple players the Dungeon Guardian will die faster.
 * If you're using a gun, Chlorophyte Bullets will home in on the guardian to maximize damage.
 * 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.
 * Due to being invincible to direct damage in the tutorial on console, it is possible to survive all attacks from the Dungeon Guardian. This, however, is not the best way to defeat him as one; you will be knocked around incessantly without a cobalt shield making moving a challenge and two; the absurdly high defense of the Guardian makes it nearly impossible to kill him.
 * If you're lucky enough when wearing a Black Belt or Master Ninja Gear, you may be able to dodge its attack.
 * It is possible to survive a hit from Dungeon Guardian using Beetle armor (with 3 beetle charges from beetle shell) and Lifeforce Potion (with maximum life), the damage can be reduced further with high defense and defensive potions.
 * You can become invincible with the Valentine Ring and Spike. After you lure the Dungeon Guardian out of the dungeon, you can go to a field of spikes previously set beforehand. The spike will deal 1 damage, but will be quickly replenished with the valentine ring. However, this can only happen if you are wearing Hardmode armor like the Turtle armorr.
 * If you are in multiplayer, if 4+ players have turtle armour its enough to kill a guardian using the turtle armour bonus.