http://www.newgrounds.com/portal/view/621683
Futanari Trixie fucks Rainbow Dash!
That quotation says it all. This game is by ButtercupSaiyan, Mittsies, and Suddensharpintakeofbreath.
Just click the “Next” button in the upper-left corner to advance the situation, and follow the dialogue (or minimize it) in the lower-left corner.
Well, the premise is Nightmare Night, but other than that I have no idea. Still, it was oddly arousing. The music is…sufficiently appropriate.
EDIT: Just a minor note, you can click Trixie’s hat to change it. Just found that out.