Laughing Zombies.

His "zombies" as they are called, are increasing day by day. Both the living and the dead succumbed to his infection so his zombies only increased in number. Their numbers increased from millions to billions very quickly. 

It was a losing fight for the inhabitants of the plane. More gods died to the tide of zombies so Legion-7 got his hands on the domain of illusion and death. However, the two domains didn't increase his abilities as much as he thought they would. 

The domain of illusions made it easier for him to possess his targets by reducing their resistance through illusions. The domain of death made the souls of the dead converge onto him. He gained the ability to pull souls to himself like the fragmented Origin gods but he wasn't impressed because he doesn't need it anymore.