Although Shadow Lugia is not available for capturing in the normal gameplay of "Pokemon Platinum," you can obtain a Shadow Lugia using a unique cheat code with the Action Replay DS device. The Action Replay devices allows players to enhance the gameplay by entering a cheat code for rare or impossible-to-obtain Pokemon and items. By entering the code and walking around in the Mining Museum in Oreburgh City, you can get your own Shadow Lugia in minutes.
Insert the Action Replay DS device into the cartridge slot of your Nintendo DS console and attach your "Pokemon Platinum" game cartridge to the Action Replay DS.
Turn on the Nintendo DS console and navigate to the "Games" folder in the Action Replay main menu. In the "Games" folder, find the "Pokemon Platinum" game folder and press the "A" button on your Nintendo DS to continue.
Scroll down to the "Add New Code" option on the menu and press the "A" button. On the next page, give your new cheat code a name.
Enter the following "Shadow Lugia" cheat code into the text box:
Press the "Start" button on your Nintendo DS to save the cheat and launch the "Pokemon Platinum" game. On your saved game is loaded, use your Pokemon's "Fly" ability to travel to Oreburgh City.
Travel to the north-east corner of Oreburgh City where the Mining Museum is located. Enter the Mining Museum and walk around until you encounter a Pokemon. If you have entered the cheat for Shadow Lugia correctly, the next Pokemon you face should be Shadow Lugia.