I guess nothing with really big appendages [Wings, horns, etc.], or two forms [werewolf, shapeshifter etc.] or too high-fantasy [Coloured skin, etc.]-- want to be able to blend in with the civilians, after all.
We allow some slight magic/elemental manipulation.
We'll actually have forms and stuff later on when I get around to writing them, so that'll give a clearer idea of what we're looking for. u vu