This story is based on Thunderstarwarp's Stars Dashingand Friendship is Magic: When All Are One. I have his permission to write this so long as I tell you to read his stories to understand how it is that Starscream has been ponified, and that this is a non canon work meaning that while it's based on his work it is not a part of his plot line.
The easy way to think of it is to say that this is like a DBZ movie. While the characters derive their origins from the series the movie never effects the flow of the series, but you do have to be acquainted with the series to understand the movies. This particular tale is seated between the two fics listed above, so at the very least read Stars Dashing.