Well I got a friend that has an action replay and he is raiseing his pokemon only by rare candy and he wants to battle me would he be a threat ?
If he raised all his pokemon only by rare candy and you were doing lvl 100 or lvl 50 single/double then no becuase his pokemon would have no evs what so ever thus significantly weaker as a matter of fact 127.5 stats points per pokemon weaker(in total for a team thats 765! so if you ev train your pokemon he will get his butt kicked)
It really depends. If for example he uses Rare Candy to have his Pokemon a higher level than yours, then yes, those Pokemon would be a problem. Nothing a good old FEAR technique couldn't fix though.