Subjects of Equestria! We are pleased to kick off the Nightmare Night Festivities and the 14th anniversary of the return of our beloved Princess Luna! Join us in celebration!
It looks like some kinda fancy light effect for emphasis, but for some reason I get the impression that Mistress Marevelous is either appearing or disappearing in a puff of smoke from a smoke bomb. Nice. I can imagine Marevelous carrying smoke bombs around for a quick/showy exit.