Things You'll Need
Instructions
Place the Action Replay into the Nintendo DS game cartridge slot. Insert "Pokemon Platinum" into the tip of the Action Replay.
Turn the DS on. Choose "Pokemon Platinum" In the "Games" section of the Action Replay.
Select "Add New Code." Select "Next" to continue. Insert the following code to unlock Shadow Lugia:
94000130, fcffoooo, 38461097, foooooc, 37591610, cooooof, d2000000 and 000000.
Select "Next," then "Start Game" to start "Pokemon Platinum." Open your saved game. The next Pokemon you will encounter will be Shadow Lugia.
Attack Shadow Lugia with one of your stronger Pokemon until you have significantly weakened it. Throw a Pokeball at Shadow Lugia to catch it. If it does not work the first time, then do it until it works. Save your game once you have captured Shadow Lugia.