Kat/Goldie
Kat will be there! She'll be in her natural mer form most of the night given the nature of the event, and even have seashells on her bikini top to make her appearance seem more like a costume. To mundanes and people she doesn't know she'll be lightly projecting with her telepathy that it really is all just a super fancy and very expensive prosthetic. Those 'In the know' will likely realize her tail is the real thing however, and anyone with telepathy will know what she's doing.
She'll spend time in the dunk tank, and likely be either in the pool or hanging out by it most of the rest of the night.