I'm looking for this story where this girl goes to halloween party, and I remember there's a girl dressed as Harley Quinn and a guy dressed as pyramid head. A witch is at the parry and she turns everyone into what their costume is. The girl meets a slim guy in a Totoro onesie and then she goes home with him after the party. She then sleeps with him and in the morning, she wakes up next to a fatter version of the guy as he only ended up slim because of the witches magic. Hopefully someone knows this story, I've tried looking for a while but just don't know the name.