what do i wear to a mardi gras ball?

I'd assume you know someone else going in order to get the invite, you should probably ask them. But since its a ball and everything, I'd throw a wild guess out there and say you need to wear a tux. Date needs to wear a ball gown, but I don't know what that entails. If she's 18 that means she's probably been to about 45 dances/proms/events already and knows exactly what to wear.