It's hard to say how aware the glambot is of what's happening. Perhaps he's committed to the bit to save his own sanity, perhaps he's being controlled. It's a dreamscape so maybe it's a bit of both.

Whatever the case, Mettaton appears to be part of one of the main performers for the ball. His outfit, the various songs he performs... It all seems rather on the nose for how certain parts of the castle appear and the overall atmosphere of the event. (Does he even know what his outfit is from?)

He certainly cuts a striking appearance in that outfit though, even donning a matching mask for when he's mingling with the crowd. Which, in between sets, he's more than happy to chitchat or even dance. Should you approach, he offers an ever-so charming smile along with a bow.

"What a pleasure to see you here, darling! I hope you're enjoying yourself?"