Pokémon XD: Gale of Darkness/Cheats

Sure Spare 1 HP Attack
All you need is a pokemon with the False Swipe attack. The Zangoose that you snag from Zook has learned it. A Pokemon with this move can almost always leave any opposing pokemon of lower level with 1 hit point, making it an easy target for pokeballs.

Recapture Missed Shadow Pokemon
If you didn't manage to snag a specific Shadow Pokemon that you wanted, then keep fighting the Mirror B. person until you capture it.