Oh! Was that the one where she was turning every-pony into cupcakes, and was describing how she completely mutilated Rainbow Dash and turned her into one as well? Holy crap, I read that once; I thought it was pretty cool, but it was so gorey and detailed I was cringing. D; I kind of wish I could be as detailed as that when writing, but my small vocabulary prevents me from doing so.
I don't remember if I ever "finished" that story, but I remember skimming through some parts because I was too lazy to read the whole story at that time/it started becoming a bit to gruesome for me to fully read it. That story was insane! XD