Oh this sounds like a fascinating custom!
I agree with the awesome suggestion of the seaspray pose, with the head turned that will be close!
Don't get your hopes up! Will be my first custom and I have no artistic talent at all, so it's gonna be very simple!
Though, if I ever make it to the level of some of the customizers here, I may revisit this and actually do a "Mirror" themed custom - like, actually put a 'mirror' between them and have one be the crazy/scary/whatever reflection of the other.... hmmm...that would be more skill than I have, i'm afraid...