Help for a Costume Wedding

This question recently came in through the advice “line,” and it seems like a better fit for a group solution (and rings a bell, although I can’t find why that’s the case or where it appeared, so apologies if this is a repeat, and apologies for accidentally stealing others’ costume ideas). Anyway let’s solve this!

My boyfriend’s good friends with a great sense of humor are getting married very close to Halloween, and ask that we all come in costume. I’m already pretty terrible with thinking up costumes, and with the added constraints of wedding level elegance, I’m coming up with nothing. Do you have any ideas?

Historical costumes — maybe something Downton Abbey? (The mansion itself?) Fancy flapper? (Finger waves/pin curls?) Anything/anyone from the Scandals of Classic Hollywood series? If it were me, I’d probably just wear a typical-wedding-appropriate dress and carry a mask on a stick, but I’m lazy and not crazy about enforced fun. Anyway, thoughts?