Giruveganus is an important enemy when trying to spawn the Behemoth King mark, as Behemoth King shares the same spawn-point. To spawn the Behemoth King, the player must kill the Giruveganus in Edge of Reason, then move to Ice Field of Clearsight and clear all enemies, and Behemoth King will spawn in Giruveganus's place.
If the player kills Giruveganus in Edge of Reason, leaves the zone and returns, there will be no enemies in that area (other than Behemoth King if spawned).
Being a tyrant-wyrm driven to madness by Mist; now a violent, capricious creature. The naturalist Merlose writes, in one of her most harrowing accounts: '...that hideous Mist which spilleth forth from its dark core raiseth a mirage before the eyes, and I am blind with fear and apprehension, for its nebulous form is madness incarnate. I pray that my skill with the blade faileth me not in this most dire circumstance.' Its eyes shine with a curious luminescence, allowing it to see quite well in dark, underground corridors.
Tis the height of folly to brandish arms against a tyrant that has no more form than a mirage. The broken greataxes left by those who tried and failed should be proof enough of that. In order to truly defeat a foe, one must know more than the foe's character and physiology. One must listen to what the dead have to say on the subject. No one wants to be next in line to have their greataxe broken.