Wow!
Gargoyles – eliminate them, since they can’t draw normal monsters, only boxes.
Gremlins – leave them for the sake of humor, but give the upgraded ones a funnier-looking hat.
Djinn – leave them, they’ve always been wizards...
Mages – leave them, but change their appearance from an Eastern Cossack in baggy pants and a turban to a decent, neatly dressed magic professor.
Rakshasas – the idea is not bad, but nagas are more familiar, so you can leave them.
Titans – again, we don’t need half-naked black men!
This is just about the appearance.:)