nickthedog: no, its not true. tell whoever told you that they suck. lol.
i don't know if it works on here as well as colosseum, but theres a masterball cheat.
you must be in a double battle, have a masterball, and be against a shadow pokemon.
1. make 1st pokemon use masterball on shadow pokemon.
2. make second pokemon go in the bag and switch the masterball with any other ball in the bag. then exit the bag and attack as normal.
3. the masterball will be thrown, and you will catch the shadow pokemon without fail, but the masterball will still be in your bag. none of the pokeballs in your bag will have been used.
i dont know if it works on xd, but it does on colosseum.