Forever Cosplay by Hank the Bobcat (Archive Link)
Really nice story about two women trying to get their Halloween costume to the next level, by using some spells from a spell book. It just turns out, that the spells actually involve a bit of dark magic, which causes the costumes to be a bit more difficult to remove, than the two would like.
This has a second part by a different author: Forever Cosplay 2 by jeffapr202006.