Cerberus

Cerberus is an odd hero. He has very low cost but is intent on killing himself, while drowning enemies in a high damage AoE. His ultimate gives him a sizable damage increase which, when timed with his death, can push his damage through the roof. On top of this, he is great with both his factions, making the most of the Chaotic damage buff, or providing some AoE slows at A1. Although niche, Cerberus deletes large groups on his own, making him surprisingly useful even when you manage to keep him alive.