Knowing about Rainbow's sex life, Twilight gets very curious about one thing. She wants to see if Rainbow would go through with the challenge she has in mind. This would sure be a lot of fun for the both of them. Twilight lets Rainbow know about her challenge which automatically gets accepted. The amazing athletic pegasus knows she's good at everything that involves sex, or so it seems.

Both ponies know that Rainbow is a lesbian, so Twilight makes sure to just include mares, not wanting to make Rainbow angry. This is perfectly fine, though, since Twilight knows a spell that can give the visiting mares giant horse cocks.

Twilight will have Rainbow do the challenge in a public hotel in Twilight's room that she booked just for this challenge. The hotel is gladly a mare-only hotel. Once the pegasus gets put in bondage in the middle of the hotel room with the door wide opened, she has one very simple task: endure what will be the biggest back to back pounding for a certain amount of time.

The good thing is that the mare-only hotel is packed with mares. Anypony who walks by can see what a little cute slut Rainbow is, being completely vulnerable and on full display, ready to take whatever pounding the mares can give. That's easy for the cockiest athlete in Equestria who can handle anything, right?

Who said it was going to be easy?