Why is "Rwyt ti'n ar y teledu" wrong? Why is the yn -> 'n not needed?
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
Why does 'Ti sy ar y teledu' not work here, as an emphatic sentence?
There is no reason for it to be emphatic.
'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?
Why "dych chi" but not "wyt ti"? both are "you" in English.
I've just used "rwyt ti" and it worked.