What about shape shifters, witches/wizards, and (this one is something I came up with and what seppy originally was created to be) Spirit Demons - they aren't actually demons but are considered evil because a human form isn't their true form.. Each Spirit demon is given their own creature to transform into.. No creature can be used twice (since there are multiple creatures out there can be fictional or non-fictional)
Sephtis for example has the spirit of a dragon.
Meko(another character) is a wolf
Ry → Cat
Nex → Fox
Corvus → Crow
In their human forms they have similar things to their creature, Sephtis has his eyes of the dragon, Meko has her hair color and personality, Corvus has his beady black eyes and hair, Ry has her cat eyes and a cuddly personality.. Nex is tricky and has his hair (red and black) like his creature