Easy Catch
[Note,this will only work after you get the Master Ball]When you're in a battle and there is a Shadow Pokemon,don't worry about it and kill the other pokemon.For you're 1st pokemon's move, go to items and go to the Balls section.Then select any ball, in this example, a poke ball.Then use it on the Shadow Pokemon.Fo you're 2nd pokemons move, go to items and go to the Balls section.Then select the Master Ball and use it on the Shadow Pokemon.You should end up using the poke ball and catching the Shadow Pokemon without FAIL