One of my favourite characters in terms of personality is Dr. Fusion.
She has vast knowledge of chemistry and biology, and has used her knowledge to combine several creatures to make monsters. She also has access to dangerously acidic chemicals and can use them as a weapon by herself. She finds herself questioning her fellow villains (and her own boss's) decision making, and is always the first one to call somebody out.
Francesca has the most accessories I've added to a character so far, with her belt (where she keeps her concoctions for quick access) her gas mask, her vials, her sandals (to go with her socks of course) and her glasses.
She has a really dry sense of humour, too. Something I hope the viewers will like.