If you're a fan of maces in the game, then you should get the mace of Molag Bal. Like most Daedric artifacts, the mace of Molag Bal requires you to take a quest for the Daedric prince.

Skyrim players are theorising ways of doing Molag Bal's quest without doing anything morally reprehensible. There's an exploit you can perform to save Tyranus' life during House of Horrors.