Dungeon Guardian

Dungeon Guardians are enemies that guard the Dungeon against intruders. If a player enters the Dungeon without first killing Skeletron and travels below zero depth (a horizontal border separating the surface from the underground), one or more Dungeon Guardians quickly fly at the player, dealing 1,000 damage each, which effectively kills most players instantly. Dungeon Guardians are large, very fast, and travel through all blocks.

Any player attack on a Dungeon Guardian, regardless of the weapon or other equipment, will deal only 1 damage, or 2 for critical hits.

Dungeon Guardians are immune to the Poisoned, Venom, On Fire!, Cursed Inferno, and Confused debuffs.

Tips

 * Killing a Dungeon Guardian is possible, though it would take thousands of hits due to its absurdly high defense. Combined with the fact that you generally need to contend with multiple Guardians at once, victory is extremely unlikely unless you prepare carefully for the encounter.
 * Using full Turtle armor (for damage reflection) and the Black Belt (for dodging) can make killing a Dungeon Guardian more plausible, though one must expect a number of deaths before being successful.

Trivia

 * Originally, actual Skeletron Heads were used to guard the Dungeon. Killing all Skeletron Heads would count as defeating Skeletron, so the Dungeon Guardian was created to repair this unintentional behavior.
 * Despite being intended to be unbeatable, it is not invincible like Spike Balls and Blazing Wheels are.