I'm going as Snake-Lady, Lady Viper, The Asp from Neon, Python-King's Concubine, The Hissing Lust...take your pick.
For mask, I'm using something from my original equipment. Snake skin mask. Tight, shiny, and leathery. For costume, also tight snakeskin under toga. Kiph is a woman for the puprposes of the ball. He's very skinny and slight, so it could work. Fake boobs, foam by hips, wires, peepee tucked away, good make-up job under mask, just in case, and all those other necessary woman thingies, courtesy of Helena's help.