This means the page will walk you through a specific task, strategy, or enemy/boss fight.
The Dungeon Guardian is statistically the strongest enemy in Terraria, and only spawns when you move below 0 depth in the Dungeon before defeating Skeletron. Once Skeletron is defeated, Dungeon Guardians will no longer spawn. There is little reason to fight it, except for the Bone Key it drops, or for bragging rights. A good way to beat it is to have multiple 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 multiple players is so someone can always be alive so it doesn't despawn.
Terrain Preparation
A skybridge used for killing Dungeon Guardians. A 'stairway' allows the player to quickly ascend to the skybridge when the Guardian has been summoned.
As it will (almost always) instantly kill you when it touches you the only way to defeat it is to outrun it. Therefore you have three good options for terrain. First is simply use the whole map, by using Gravitation Potions to move around. You will fall faster than it 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 and jumping with wings. If you want to outrun it make a diagonal skybridge (any blocks except platforms work for this) or build the skybridge out of Asphalt. The third option is to use the Phantasm with Luminite Arrows and a Cosmic Car Key and move in one direction until you kill it. 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 required for the player to bring materials from a world where Skeletron has already been defeated.
You can make a large pathway made of Ice Blocks and use Ice Skates or Frostspark Boots
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 even if Frostspark or Lightning Boots are used, however jumping with wings occasionally allows you to keep up with the Dungeon Guardian's speed.
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. It is recommended to maximize your critical damage to finish off the Dungeon Guardian much quicker.
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. On the 
Mobile version, the Dungeon Guardian's defense is ineffective against Frostburn, and even seems to amplify its damage, so this is a great option. 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, S.D.M.G, Vortex Beater 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. Any weapon comes down to 1 or 2 damage so using faster weapons help. Be sure to bring plenty of ammo; two full stacks should be considered the bare minimum. The Endless Musket Pouch is very useful in this case.
- Bows that may be useful are the Tsunami or Pulse Bow, due to them firing multiple projectiles. Combine them with Holy Arrows or Heart Arrows for more damage (which is mainly useful if you do not make use of the skybridge method). If the player happens to undergo the Lunar Events, the Phantasm is, without a doubt, the prime bow to use because of the ability to fire a continuous stream of arrows, as well as a 66% chance not to consume ammo. Using this bow with Holy Arrows or Frostburn Arrows is a great strategy.
- 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, Terra Blade, Solar Eruption, the Possessed Hatchet, or the Flairon are possibilities.
- 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 Stardust Cell Staff or Stardust Dragon Staff to do lots of damage while the player concentrates on dodging.Any bow using Heart Arrows, because Heart Arrows will stun the Dungeon Guardian, giving you time to maneuver.The Cosmic Car Key and Seedler are a great combination to use when defeating the Dungeon Guardian, since Seedler will throw explosive seeds. It will take around 5-10 minutes if you yourself don’t miss too many hits on the Dungeon Guardian.
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 a 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, the Solar 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 or it's upgrades, 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, Paladin's Shield or Ankh Shield will prevent enemies from knocking you into the Dungeon Guardian.
- The Cosmic Car Key can be used to outrun the Dungeon Guardian as its speed is the same as the guardian's.
- There is also a glitch you can perform with the Slime Mount that allows you to constantly bounce on the dungeon guardian but not take damage even if you're being pushed up in to a wall.
- The Rod of Discord is also quite useful as if the Dungeon Guardian gets too close, you can teleport to a safer distance.
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 Potion, Night Owl Potion and Shine Potion.
- A Summoning Potion can be used to allow the usage of an extra minion.
- An Ammo Reservation Potion is great for saving bullets therefore increasing damage.
Bullet-spammer Method
- Obtain both a Cosmic Car Key and a Megashark or Chain Gun, as well as a good pair of Wings. Go to the dungeon and dig straight down (depth meter or upgrades are handy here). When the Guardian spawns, use your wings to escape, at which point you activate the UFO mount from the Cosmic Car Key to kite/lead the Guardian around, while attacking with the gun. A flying minion is recommended as well as scouting out the surface.
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. Also, if you use a Yoyo, it will stay out, even if it has a limited flight time.
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.
Heart Arrow & Summon Method
Armor & Accessories
Heart Arrow x ~9000- Chlorophyte Shotbow/ Tsunami
- Wings
- Tiki armor or Chlorophyte armor
- Pygmy Staff
- Pygmy Necklace
- Necromantic Scroll
- Papyrus Scarab
Terrain
This method is great if you don't especially like terrain preparation, for the only thing you will need to do to the terrain is build a stairway of asphalt leading out of the Dungeon or if you have the Lightning Boots they can be used on a dirt stairway.
The Battle
First summon all of your Pygmies then go into the dungeon just far enough to summon the guardian. Once the guardian has spawned go up your stairway and onto a flat area. Then begin to shoot the Guardian with your shotbow. It should completely freeze in place. Continue shooting it with your heart arrows and your Pygmies will throw spears. Also if you have anyone who could join your world to help with the fight they could use a magic, ranged, or fairly large melee weapon(keep your distance!) to make the fight go much faster.
Heart Arrow Frost Armor Method
You Will Need:
Preparation
Make a house near the dungeon and make a hole down into the dungeon.
The Battle
Jump into the hole and Magic Mirror home (near the Dungeon) and run a few blocks from your house. Using Frost armor, you can do 32 damage per second through the debuff. Using heart arrows will stop the dungeon guardian and the Chlorophyte Shotbow/Tsunami will fire multiple arrows at the dungeon guardian, killing it faster. This can be achieved alone and you will kill the dungeon guardian in less than two minutes, if not less than one.
Mechanical Cart Method
If you have killed the three Mechanical Bosses in Expert mode, you will have access to the Mechanical Cart. It can travel fast enough to easily outspeed the Dungeon Guardian but this means that you may end up despawning it. Reducing the speed is possible to allow it to keep up, however, as showcased in this method.
Therefore, you can make a long, flat minecart track to traverse across with a Mechanical Cart to combat the Dungeon Guardian at a distance. However, Something special must be done at either end of the track, or else you will simply run into him and die upon turning around. Both ends of the rail need to have the following assembly:
This works by utilizing the fact that Teleporters can "see" through rails. When you are riding a Minecart on a track that's directly over a Teleporter and it is activated at that moment, it can teleport you and the Minecart you're riding to another rail that's on top of another Teleporter, keeping your momentum in the process. The branching rail on top is set to a passive state (you pass through it on the bottom line without switching on to it). The bottom Teleporter has a Pressure Plate Track over the Teleporter to trigger it, but the top one does not. This is important, as otherwise you would instantly trigger the other pressure plate and teleport back into a facefull of Guardian. The top rail has a bumper at the end of the line to make you turn around to the other direction without losing speed.
Lastly, this only works if you are moving slowly enough such that the Dungeon Guardian is lured in between the two Teleporters upon teleporting. Otherwise, you'll simply run straight into him in the same manner of if you just had a bumper at the end of the rail.
Hoik method
This method is great to kill the Dungeon Guardian early in game, but can be done anytime. It takes awhile, so be prepared. Almost any ranged or thrown weapon can be used, but the boomerang is best, since it can be repeatedly thrown into the middle of the room. Make a large hoik loop in the main dungeon room. Make a small room with a bed on the other side of the dungeon door, and set your spawnpoint. Move below 0 depth, and when you hear the Dungeon Guardian, use a recall potion, and then use the loop. It will try to get you, but you will be moving too quickly. Just keep throwing the boomerang until it dies. This will take nearly 2 in-game days to kill the Dungeon Guardian (with a fresh character). For a more detailed explanation, see Yrimir's Dungeon Guardian on Second Night video.
General tips
- If you have wings, you can dig a hole in the dungeon deep enough for the Dungeon Guardian to spawn, and then fly up to the surface.
- 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.
- Two players are better than one, using these methods can make the fight easier, but still very hard, have a friend or two help you out, if one of you dies, then there's still two left, giving enough time for the player to respawn and continue the fight.
- 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.
- Using Minions and Tiki armor can shorten the time required to defeat the Guardian.
- Using Frost Armor with ranged or melee weapons is a good way to deal lots of damage, as the Dungeon Guardian is not immune to frostburn and will thus increase damage.
- If you're lucky enough when wearing a Black Belt or Master Ninja Gear, you may be able to dodge its attack.
- Use multiplayer. 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 accuracy, whereas Crystal Bullets will maximize damage through the shards.
- Using a Phantasm
is very effective if you want to use the Easy Kite Method, as it shoots 4 arrows at once. Alternatively, another effective bow is the Tsunami, which shoots 5 arrows at once, but is a little slower than the Phantasm. 
Due to being invincible to direct damage in the tutorial when at 1 health, it is possible to survive all attacks from the Dungeon Guardian. This, however, is not the best way to defeat it 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 it.- Another, unmentioned way to defeat a Dungeon Guardian is to use the Invincible Slime Statue method, requiring a slime statue and honey. You will also need at minimal a cobalt shield and the cross necklace. This requires more than one player as at least one of the players must be taking damage from the slimes generated by the statue. The other players stand outside of the "Invincibility Box" and attack the Dungeon Guardian(s) until defeated. May take 1-2 in game days to defeat.
- On the Windows Phone version and Nintendo version, using Heart Arrows and a Hallowed Repeater can stun the Dungeon Guardian completely.
- You can become invincible with the Valentine Ring and Spikes. 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 Armor.
- Using Fishron Wings , Frostspark Boots , Frost Armor ,and a Flairon can be an effective method to defeat the Dungeon Guardian as the bubbles home in while inflicting Frostburn. This is especially effective on the Mobile version, as Frostburn deals extra damage to Dungeon Guardians.
Trivia
There are two methods that no longer work due to updates:
Co-op Magic Mirror Method
Stopped working after 1.2 update: By far the easiest method is to exploit a magic mirror's invulnerability time. Set the spawn near the dungeon, then have one player go down into the dungeon and lure the guardian out. Spam the magic mirror and the dungeon guardian will hover over the player while a second may stand near and use a fast weapon such as the clockwork assault rifle, bananarang, or bladed glove. Minions can be used to achieve the same effect in singleplayer.
Co-op Kamikaze Method
Stopped working after 1.2.3 update: Two players with full Turtle armor should walk into the dungeon very close to each other. A Dungeon Guardian will spawn, killing both, but the Thorns effect will kill the Dungeon Guardian. One player returns, recovers any lost items and the Bone Key, and uses a Magic Mirror to escape. This is one of the most recommended strategies to kill the Dungeon Guardian because it is the fastest way to do so.
