Evendim
Evendim is an epic boss found in Syrtis war zone. His fightstyle seems quite balanced (and dreadful), mixing area health and mana drains, powerful normal hits, and very strong close and long range spells.
In order to defeat him, players usually take advantage of the Stonehenge like structure in the area. Ranged classes bombard him from all sides to keep him distracted and aggroing different players, making him go back and forth in the middle of the circle. Warriors have to make runs to attack and quickly retreat in order to avoid being obliterated by aggroing him. Also, if a lot of them stand close, they can waste everyones efforts by being target of mana and health drains that completely replenish the monster, while dealing damage to everything around.
Although he it isn't confirmed to be, he is sometimes thought to be the hardest epic boss in the game.