Shadow Lugia:

Shadow Lugia, codename XD001, is Cipher's ultimate Shadow Pokemon. In this game, the boss, Grand Master Greevil, is planning to take over the world by completing a Shadow Pokemon army, and their Lugia is the star. How do you capture such a powerful creature? After talking to Prof. Krane at the Pokemon HQ lab, you'll receive a Master Ball. Save it until you get to battle XD001. In Citadark Isle, you must battle all three of the admins, including several trainers, in order to defeat Grand Master Greevil and Cipher itself. The final part of Citadark Isle is a sphere-like dome. Once you enter it, you will encounter Shadow Lugia. Catch it easily with the master Ball and then take down Greevil's Pokemon. Shadow Lugia, unlike any other Shadow Pokemon, cannot be purified by giving it scents, walking around or battling with it. You need to use the Purification Chamber. Every part of the chamber must have a maxed out tempo. After purifying it, it becomes a normal Lugia. It will be at lv. 50 with its original 'shadow' attacks (Shadow Blast, Shadow Down, Shadow Shed, and Shadow Storm) removed and replaced with Lugia's common attacks such as its very own signature move, Aeroblast. If you haven't decided to purify your Lugia yet, then you should know how it works in the game. Unlike any Shadow Pokemon, its gauge will not decrease by clearing its anger, and it won't level up not matter how much to try. Also, it is not allowed to be used in the Orre Colosseum and cannot be traded to a GBA game if its not purified.

Facts:

Lugia, unlike any other Pokemon under the control of Cipher, actually wants to be set free from its evil state. XD stands for Xtra Dimension. Shadow Lugia's nickname is XD001 probably because it is the first Pokemon that cannot be purified in the shrine of Agate Village, let alone with a Time Flute, which might be what the '001' stands for. Pokemon XD: Gale of Darkness was a Nintendo GameCube best seller.