User blog comment:SwifterGUY1/Dungeon gaurdians is there any way to kill them?/@comment-4674838-20120706152338

Yes, it is technically possible to kill a dungeon guardian. But you have to spend 15 minutes flying around with a Gravitation Potion doing a measly 1 damage per second with your ranged weapon of choice. They don't drop any loot. Oh, and when you kill the dungeon guardian and go to enter the dungeon, another dungeon guardian will spawn.

So, while it is possible to kill the dungeon guardian, there isn't a practical reason for really doing it. It's mostly just a bragging rights sort of thing.