Xoggoth

Aura of Corrosion reduces your attack and magic damage based on total amount of damage you have dealt to the unit so far.
Cloud of Death may kill some of your units instantly. Chance of being killed grows with total amount of damage you have dealt to the unit so far!
Unit's anger causes splash damage which hits every single member of your army. Rising total damage dealt to unit makes Explosion of Anger hits stronger than before!
A brutal, villainous and wicked ancient deity. His names include such titles as 'the Keeper of Darkness', 'the Devourer of the Living' or even 'He who walks with Death'. According to the scriptures, this malevolent deity was considered to be long dead. He has apparently regained some of his power and seems to be particularly obsessed with obtaining the Tears of Gods.
"...and on the final day Death will arrive. Without questions, without forgiveness, without mercy, the Keeper of Darkness will devour all. And Darkness will reign for eons to come."
The Prophecy of Akul-Tun, The Book of Black Sermons