"You are on the TV!"
Translation:Dych chi ar y teledu!
Because "ar" is a preposition. You don't use "yn" + preposition. "wedi" is also a preposition, which is why it's "Dw i'n mynd ennill" but "Dw i wedi ennill".
The proposition yn (or 'n) is usually followed by a verb when used in this manner, and that is not the case with this sentence
'Damn, YOU are on TV!' sounds very emphatic to me chuckles Anyway, if I WANTED it to emphasize the YOU, would my construction have been correct or am I way off the mark?