Titan-blooded halfling Wu Jen/Eldritch Knight. Start as a small creature wielding a gargantuan warhammer. End up as a colossal creature with a warhammer four size categories above colossal, dealing 36d6 damage a blow.
any outsider from dnd 3.5 (tiefling or aesimar) + alter self and polymorph to transform into other outsiders and with polymorph you don't need to be familiar with what you want to transform into...just a classic horrible combo. I had one a tiefling sorcerer doing that all day...that wasn't right.