Vanity and self loathing go hand in hand, gaze at one self within the mirror and you can fool yourself to be something you've always wanted to be..
Mull is selfish and insecure about himself, he comes from an abusive background..
Mull is the son-one of many- of a very powerful Demon, but Mull always wanted to be an Angel..however, what Mull doesn't know is that he's a halfling..