I was more using Ouroboros as the alchemists' snake and rolling with the whole turning metals into gold thing. I figured the other goal of alchemy, immortality, would be way too OP, so I scaled (pardon the pun) that back to an invisible armor covering his body. You're right though that Ouroboros usually has to do with immortality or time. I can change him to more of a "Oh you just blew my head off? Well screw Death, I'm gonna go ahead and rearrange your face now." type of character if you want me to.