As a classicist I love the kind of obscure mythological beasties included in various metroidvanias--like Catoblepas, Amphisbaena, Amduscias and all the Ars Goetia dudes--though I'd like to see their sprites updated occasionally, Cato has the potential to be really bizarre and Glasya Labolas could have been cooler. I'd also like to see Blackmore again, he intrigued me, and the Frozen Half. And Carmilla and Laura always have a place in my heart.
Along these lines, what enemies did you like, who do you want to see get a facelift, and what mythological critters should be added?
My ideas-
Crocutta--magic using were-hyena.
Emim/Rephaim--biblical giants, though perhaps just other tribes in reality. emim apparently meant 'dreadful'. Undead golem types? Emim the stronger palette swap?
http://en.wikipedia.org/wiki/RephaimChrysaor--Other thing created by Medusa's death besides Pegasus. I'd like to see it as a massive winged boar rather than the more boring dude-shape.
these have probs all been in SMT/Persona, but you know what, so has /everything/ so what can you do.