Day - Queue — LiveJournal
I get the feeling that costumes are strongly encouraged but not mandatory.
Speaking as one of the (presumed) hosts of the party in question, I too get that feeling. Costumes are great: they add to everyone's fun, and they're traditional for Halloween, of course. But I would rather my friends came costumeless than not at all -- by a longshot.
We do have one or two costumes kicking around we won't be using, by the way, so if you show up and they're not claimed yet, we can kit you out. So come in any case!