Here's why:
* AR Codes and SoulSilver: Pokémon SoulSilver doesn't use AR codes the way newer games do. It utilizes cheat codes, which are different.
* Mewtwo's Armor: Mewtwo's "armor" is part of its design in later games, not something added in SoulSilver. It doesn't exist in the game's code.
* Game Modifications: While you could potentially modify the game using hacking tools, it's a complex process and goes beyond the scope of simple AR codes.
To get Mewtwo in SoulSilver:
* Trade: You can trade a Mewtwo from a newer game to SoulSilver.
* Cheats: If you're using a cheat device, there might be codes to obtain Mewtwo, but it won't have the armor.
Remember, using cheats can compromise your save file, so proceed with caution.