Past Sins is one of the most popular fanfics in the My Little Pony Friendship Is Magic fanbase. Months after completing the story, its author Pen Stroke decided to give various writers from the /fic/ board on Ponychan a chance to riff the original, previously unseen and unrevised version of the story. Readers from the Equestria Daily fansite were also recruited to add riffs of their own. The result is an MST, which can be found here.