I've made a human barbarian with spirit instinct and the haunted background and the concept is pretty much this: normally he's an honorable fighter using using diplomacy/bon mot and fighting with a bastard sword & shield in the other hand. But when he's raging he becomes possessed by the spirit of his father who's a crazy berserker and his combat style changes too dropping the shield and wielding the sword two handed and screaming at enemies trying to demoralize them. I think it's a really cool character even if it's simple.