"Dych chi wedi mynd? Nac ydw."

Translation: Have you gone? No.

[Salsmachev]

Is this as in, "I just got back from seeing that movie, have you been?" Or more like "How have you been?" or what?

[rmcode]

It should be 'Have you gone, No(I have not)' as the best translation, someone altered it to a more natural sounding sentence in English but this obscures the meaning. That's been changed back now.

It could be interpreted as either 'Have you gone (there), No (I have not)' or 'Have you been (there), No (I have not).

Hope that makes it a bit clearer, thanks for the comment.

[KarolkaR]

Technically, this is not past tense but perfect tense.