Based on the classic number from Disney's Fantasia, this is my take on what would happen if Sweetie Belle tampered with a spell far beyond her capabilities. The ensuing chaos forces her to try and stop it before it's too late.

A big race has come to Ponyville and everyone is excited. Rainbow Dash seems to be the winner for sure when a new pony enters the race. With her reputation of the fastest pony on the line, tensions rise between them. However, this is no ordinary race.