The Dungeon Guardian is statistically the strongest enemy in Terraria (if not counting invincible enemies), and only spawns when you move below -3 (underground) depth in the Dungeon before defeating Skeletron. Once Skeletron is defeated, Dungeon Guardians will no longer spawn. The only reason to fight it is for the Bone Key it drops.
You need to be in a world where Skeletron has NOT been defeated. Otherwise, it will not spawn.
As it will instantly kill you when it touches you, the only way to defeat it is to outrun it. Therefore you have five good options for terrain:
- The first option 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 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 or build the skybridge out of Asphalt.
- The third option is to simply use a good pair of Wings or a flying mount such as the Cosmic Car Key, Witch's Broom (Expert Mode only) or Shrimpy Truffle with a clear, open space.
- The fourth option requires a rail system that goes in a circle, using a fast Minecart (Using mechanical Minecart is more useful) or Booster Tracks. This can also be automated with Traps, such as Spike Ball or Spear Traps within the rail circle of with summons and a Star Wrath.
- The fifth option is to set up a Hoik loop. As the Dungeon Guardian spawns use a recall potion to get to a spawn point set up near the Hoik loop and mount it. If timed correctly, you will loop around fast enough to make the Dungeon Guardian constantly change direction, and, as a result, simply spin in tight circles in the center of the Hoik loop.
To reliably "summon" the Dungeon Guardian, it is recommended to dig a straight shaft down from outside the dungeon. The Depth Meter or any of its upgrades are 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.
If using magic weapons, the Spectre Armor with the Spectre Mask will release extra projectiles which will deal even more damage to the Guardian.
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. Hallowed armor's Titanium armor's set bonus allows the player to survive a hit every 30 seconds.
Because of its massive defense, no weapon will deal more than 1 damage (2 with a critical hit), so it is much better to use weapons with a very high rate of fire or multiple projectiles. It is recommended to use any prefix that increases critical hit chance or firing speed.
- For Melee users
- The Flairon releases many bubbles when used, which can deal rapid damage to the Guardian.
- The Vampire Knives, the Scourge of the Corruptor and Seedler are useful due to their multiple projectiles and fast rate of fire.
- Solar Eruption has great reach and hits many times when used.
- Though very late into the Game, The Zenith provides a long range attack, whilst each sword deals hits, allowing for consistent, rapid damage to the Guardian
- For Ranged users
- The best guns are the Chain Gun, S.D.M.G, Vortex Beater, Megashark, Gatligator, Minishark, or Uzi, listed in decreasing order of effectiveness. Combine them with Crystal Bullets for additional damage from the released fragments.
- The best bow is the Phantasm, with the Tsunami and Eventide as passable alternatives. Combine them with Holy Arrows or Luminite Arrows for more damage.
- The Piranha Gun is very easy to use and deals damage at a fast rate.
- A bow with Heart Arrows stuns the Dungeon Guardian, making the fight a lot easier.
- For Magic users
- Some of the fastest magic weapons include the Razorpine, Laser Machinegun, Bat Scepter or Blizzard Staff.
- The Lunar Flare has a very high fire rate, along with a high critical strike chance, making it another useful weapon.
- The Nebula Arcanum can hit a lot of times if used correctly.
- The Last Prism can also be used effectively, however you might need to use a Mana Flower and a large quantity of super mana potions.
- For Summoners
- The Stardust Dragon Staff, Xeno Staff, and the Terraprisma deal damage at a very fast rate. The Blade Staff, however, seems to perform the best due to its very fast attack speed.
- For Throwers
- It is not recommended to use throwing weapons against the Dungeon Guardian, due to its high health and the fact that you will need many stacks of whatever weapon you are using. As such, it is best to use another class such as ranged.
- Beenades are the best choice, due to the bees that they create, which can hit the Dungeon Guardian multiple times.
- Spiky Balls and Bones (even without the Bone Glove) are also strong choices.
As the Dungeon Guardian will instantly kill you, your defense is entirely irrelevant. For this reason, it is recommended that you use mobility accessories rather than defensive ones (it's possible to survive up to 3 hits with enough defense, damage reduction and a lifeforce potion, this however comes at the cost of damage output and mobility, making it unlikely to succeed without the use of teleporters, minecarts or some other mobility method). As with weapons, prefixes that boost your critical strike chance or movement speed will be much more valuable than damage or defense.
- The best Wings to use are Fishron, Solar or Stardust Wings. The Hoverboard, Celestial Starboard, Betsy Wings, Vortex Booster, and Nebula Mantle have the ability to hover, which is very good as well. With any type of wings, the Frog Leg is very useful because it provides 50% increased flight speed.
- If you are in Expert Mode, the Soaring Insignia grants infinite flight time, which is invaluable during this fight.
- Master Ninja Gear gives you the ability to dash, as well as a chance to dodge a hit.
- The Destroyer Emblem and Eye of the Golem increase critical strike chance.
- The Pygmy Necklace, Necromantic Scroll and Papyrus Scarab increase the maximum number of minions.
- If you use a Skybridge, a Cobalt Shield or better will prevent enemies from knocking you into the Dungeon Guardian.
- The Brain of Confusion also gives you the chance to dodge a hit
- The Cosmic Car Key and Shrimpy Truffle are both strong choices. The Witch's Broom, while being Expert Mode only, also boasts a greater horizontal speed than that of the Dungeon Guardian
- The Blessed Apple is good if using a sky bridge.
- Another trick is to use a looping minecart track and use the Mechanical Cart as its lasers can increase dps.
- The Black Spot is a great choice due to its infinite flight.
- The Rod of Discord allows you to teleport away from the Guardian. In combination with a sufficiently fast mount, such as the Blessed Apple or Ancient Horn, the Rod of Discord has the ability to render the fight extremely simple, so long as the player does not accidentally teleport into the Dungeon Guardian or wait too long to teleport away from it.
- 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.
- Rage Potions increase critical strike chance for all classes. An Ale or Crystal Ball will increase it further for Melee and Magic weapons respectively.
- Potions that provide light, such as Hunter Potion, Night Owl Potion and Shine Potion allow you to see better at night.
- A Summoning Potion can be used for an extra minion.
- An Ammo Reservation Potion is great for saving bullets.
Mechanical Cart Method
If you have killed the three Mechanical Bosses in Expert Mode, you will have access to the Mechanical Cart. It is faster than the Dungeon Guardian, but this means that you may end up despawning it. You should control your speed to allow it to keep up.
Therefore, you can make a long, flat minecart track to traverse across with a Mechanical Cart to combat the Dungeon Guardian at a distance.
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. 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.
With the use of Hoiks, the Dungeon Guardians won't be able to reach you, so the fight will be a lot safer. The Hoik should be the size of the first room in the Dungeon, anything bigger is unnecessary. After that, all you need to do is shoot at it or kill it with Minions such as the Stardust Dragon.
Slimy Saddle (Invincibility) Method
This method may be the easiest way to kill the Dungeon Guardian. To set up the invincibility station, you will need two Target Dummies, and a Slimy Saddle. Place the Dummies facing in any direction right next to each other. The machine must be 8 (or 7, which is optional) blocks tall, with 5 (or 4) blocks of free space between the ceiling and the Dummies. The Slimy Saddle gives temporary invincibility frames when bouncing on an entity, and since you will constantly be bouncing on the Dummies, you will get permanent invincibility. As the Slimy Saddle also deals damage for every bounce, you can kill the Dungeon Guardian while being AFK without having to use a weapon. To speed up killing the Guardian you can use weapons with high fire rate, however make sure you don't use any piercing weapons or minions and accidentally hit the Dummies, otherwise the invincibility will probably break, letting the Dungeon Guardian instantly kill you.
If you have the Cosmic Car Key, you can take advantage of the fact that the UFO mount's horizontal speed is the same as the Dungeon Guardian's at 41 mph. This means, that if you travel in a horizontal direction, the Dungeon Guardian is unable to catch you and will maintain a constant distance, allowing you to attack freely until it dies. However, the vertical speed of the Cosmic Car Key is less than 41 mph, if you travel upwards, the Dungeon Guardian can catch and kill you, so caution is required when changing direction. Because the Cosmic Car Key travels at 58 mph diagonally, you can increase the distance by travelling diagonally for a while. Reducing the distance can be done by releasing the left/right keys for a short time. It is also recommended that you use a high rate of fire gun or projectile shooting sword, like the Terra Blade, Influx Waver, or the Vortex Beater.
Shadow Jousting Lance Method
See Here for details, However, It takes quite a lot of luck and Transforming to do: https://www.youtube.com/watch?v=4KDSp-l1nbU&t=97s