...Or the perfect mare. But in this case, it's The Perfect Stallion—specifically, piano sheet music for the song. OctaviasPianist, who has shared music with Everypony Sings before, sent in another great piece. As I said, it's sheet music for The Perfect Stallion, and OctaviasPianist did a great job.
You can watch OctaviasPianist playing the song (it's awesome!) in the embedded video. Then find the sheet music here. You can also listen to a midi version or an MP3 based on the midi. After all that, you can also check out OctaviasPianist's Youtube channel!