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Actually, you have to dance around the gameboy and then Santa Claus will give you a Lugia and a free Empoleon.
Remember: You
won't get any pokémon just for beating the league
x times in any game.
Never.
And not, none of those cheats work.
The League has nothing to do with cheats so dont even bother. Lugia, get it in XD and trade it in. As for mew, your only chance is to find another real player with a legit one, check its place of capture / birth though to check if its a real one.