Cerberus

Cerberus is the Fifteenth boss you will face and its element is Fire/Earth so it is weak against Water/Spirit and it is strong against Spirit/Wind. You can face it in the Haunted Citadel or at the Summoning Stone. If you beat it 10 times, you will get the achievement Cerberus Crusher. It drops Infernal Chunks which can be used to craft Armor of the Infernal Lord  or Chimera Talons which can be used to craft Chimera Corps Uniform. Beating Cerberus on Epic stage gives access to the Kingdom of Darkness.