Instructions
Open Pokesav.
Click "edit" for the first Pokemon in the "Party Pokemon" list. This opens a new edit window that lets you edit Pokemon.
Select the drop-down menu next to "Pokemon" and scroll down until you see Lugia. Select "Lugia."
Change the "Level" stat listed below the drop-down menu you just used to 50, since Shadow Lugia is a Level 50 Pokemon.
Click on the "Name" text box and type "Shadow Lugia."
Select the drop-down menu next to Moves 1. Search for "Shadow Blast." This is one of Shadow Lugia's moves. Repeat this process for the other three Moves, and give Shadow Lugia Shadow Down, Shadow Shed and Shadow Storm.
Click on the "Edit Stats" button. Change any stat you want, such as Max HP, Speed and Attack. Click "Max" to set all of these at their highest level. Press "OK"
Change the "Party Member Allowed" amount to 1 to account for Shadow Lugia.
Press "AR DS Code Output." In the new window that appears, click "Pokemon 1" under "Party Pokemon" to indicate you changed that item. Also select "Party Member Amount." Press "Save File."
Drag this file into your Action Replay Code Manager code list for your Pokemon game. Action Replay Code Manager is free software that supports code reading between your Nintendo DS and PC. Now the next time you play "Pokemon" you can use Shadow Lugia.