I have heard rumours and seen videos of catching shadow lugia is it really a Pokemon theer really is something mentioned about revenge of greevil ........... etc.
no, there is a lugia in XD gale of darkness thats is a shadow Pokemon, but its still just normal ol lugia
In Pokémon XD: Gale of Darkness the gamecube game you can catch a Shadow Lugia and purify it or not. Either way its a very real Pokemon.