Suggestions requested for a Halloween comic! (Patreon)

I'm doing a setting of a Halloween costume party and while I've decided the appearance of some of the main characters, I'm realizing I'm gonna need to fill up some space and add in background extras, probably in silhouette just to save time. 

If anyone has any ideas for costumes to put some background characters into (cosplays off popular characters ok, but ideally I'm leaning towards "stock" Halloween costumes), feel free to sing em out, I ideally wanna get the comic ready a few days before Halloween :O