[hexen]

Depends on what you say is mainstream for a porn flick. As far as "mainstream" goes what seems to be visually acceptable as asthetic for a transformation in, lets say, a werewolf is pretty much what Teen Wolf did however when speaking of pornographic material you'd be entering another niche that is by itself already filled by sub-categories (enjoying tits or enjoying anal for example). So I'd say that there isn't really a mainstream for porn simply because porn itself isn't taken as "mainstream" and whatever floats your boat may not (and will not in some cases) work for someone else's kinks.