Things You'll Need
Instructions
Insert the Pokemon Ruby game into the GameShark or Action Replay device and insert it into your Game Boy.
Enter ̶0;0000B13000AB 1003A82A0007̶1; without the quotation marks for the master code on GameShark or ̶0;A2E564FE 0FB58A54 530823D9 16558191̶1; without the quotation marks for the master code if you are using an Action Replay.
Use the Deoxys code ̶0;88F7CB8E EE360350̶1; without the quotation marks to turn every wild Pokemon encounter into an encounter with Deoxys.
Weaken Deoxys with attacks from your Pokemon. When its health is low, use a Pokeball to capture it. Save your game and delete the Deoxys code or remove the game from GameShark or Action Replay to continue playing as normal.