I was at the Halloween Contest last year at HKTJ and I had a blast, I recommend checking it out.
As in the US some get really into the the me, some very sexy costumes, some strange costumes (devil, demon, ram), and some just put on the cat ears.
The contest itself is cool to watch but it takes about two hours (depending on the number of entries) and everyone is watching, so the mongering, socializing (and arribas) are on a sort of hiatus.
One of my best arriba experiences was with a BG dressed as an Egpytian Princess, it was a great costume and excellent conversation starter.
One word of advice if you plan to go arriba with your wife and a BG:
Most times I suggest PLs select the BG, not the BG select the PL, if you plan the arriba with your wife and a BG, go with the ones who approach your table/booth.
It means they are confortable with that arrangement and should be more fun.
Solo mis dos centavos.