if i got a charachters strength down to two and was able to use pyrophobia to return charachter to opponents hand could he use a dupe or would the charachter go into his hand and dupes are discarded

Duplicates can be discarded to save from being killed, discarded, returned to hand, returned to deck, etc. So yes he could discard the duplicate and keep the character in play.

thanks wasnt sure if they counted for backinto hand effects.

Note that if you do that in this case, the dupe saves the character from being returned to hand by the event, but not any attachments on it. The character would stay in play (sans dupe), but would lose its attachments.

This is because the attachments are also being returned to hand - separate from the character - by the event effect. It's not like an effect that says "return the character to hand," which would result in the attachments being discarded since the character never leaves play. Pyrophobia works on multiple cards, though.