If we're being perfectly honest Merlin probably has some envy in him, but what's probably more interesting is the fact that, like any other genuine feeling he has, it probably tends to be somewhat... faint or muted, compared to a normal human. So if you want something to really reinforce the fact that he isn't quite human (if Parsee hasn't already figured that out, that is) that's certainly an option!

Alternatively, there's always the fun of just getting caught up in the middle of Merlin taking advantage of the fact that he can actually use his powers again.