Well, you may want to check your Rayquaza'a stats first to make sure that it's stats are normal, and have not been tampered with. If it has abnormal stats, then you will not want it on your game. Generally, if the codes are entered correctly, Action Replay codes tend to be a little safer than Gameshark codes from what I hear, but I have no experience at all with cheating devices... if you want, compare your Rayquaza's stats and nature to the info listed on the main site, or else post it's stats/nature on here, (If you know it's EV spread, that would be great. If you don't know it's EV spread, and you have Emerald you can always save your game, and give it the EV reducing berries to get a pretty accurate idea of it's EV spread.) and I am sure that either myself or somebody else could tell you if it's stats are normal for what a Rayquaza should have. As previously mentioned, your friend may have just made up a bunch or Rare Candies and used them to Level up your Rayquaza.