Pokémon XD: Gale of Darkness/Snagging

At the start of a battle, if your opponent sends a Shadow Pokémon, the Aura Reader will activate and identify it.

Snagging is stealing tamed Pokémon. In the beginning, catching a Pokémon will be easy, but as the game goes on, you will need to take on different tactics to catch these Pokémon. Try snagging all Shadows.

The most basic of trying to make a Pokémon easier to catch is beating it down to the red zone. Be careful of moves you use so you don't accidentally defeat it. Use fixed damage moves, like Seismic Toss or Night Shade, so you don't score a Critical Hit, and False Swipe, which will always leave the enemy at 1 HP.

Another method to catch the Pokémon is inflicting a Status Condition (Paralyze, Sleep, etc.). Usually, this will weaken the Pokémon, making it easier to catch. The best Status Conditions are Sleep, Paralyze and Freeze, as they don't damage the Pokémon.

When these two factors are met, the Pokémon will be ready to catch. Try using the lowest effective Pokeball or a Premier Ball before using a strong one. If the Pokémon resists it a few times, then use a Great Ball. If that still does not work, use the Ultra Ball.

Special Pokeballs
Luxury Ball: Makes a Pokémon friendly when caught. Nest Ball: Works better when opposing Pokémon is weaker than your own. Net Ball: Works better on Bug or Water type Pokémon Timer Ball': Becomes stronger as more turns are taken in battle.

Do not use the Master Ball when you get it. It is advisable to keep it for Lugia.