During the way to become a god you will unlock the Thanatos Achievement who is the achievement you unlock when you finish the basic campaign. The boss is easy, you have just to dodger his laser beam and run on the blue aura who he let down after you hit his hand. After 3 Aura you will become a God and have to reflect his laser beam by pressing
and hit him just after, repeat this until he died. (Behind you you got some mobs who are healing or protect him I'm not sure what they do and sometimes 2 tank will spawn in front of you)