Instructions
Buy Action Replay for $15 to $21 from a store that sells video games. Make sure you buy the correct version of Action Replay for your DS. For example, if you have a DSi, buy Action Replay DSi.
Insert Action Replay into the top slot of your Nintendo DS unit. The Action Replay will click into place. Push the "Pokemon HeartGold" or "Pokemon SoulSilver" game cartridge until you hear it click. Turn on your DS unit, and Action Replay will start. Select the green asterisk button on the main Action Replay menu.
Use the D-pad on your Nintendo DS unit to move the cursor until it is pointing to "Add New Code." Select the option using the "A" button on your Nintendo DS. Move the cursor so that it's pointing to "Pokemon HeartGold" or "Pokemon SoulSilver." Press "A" to select the game.
Enter "Deoxys" as the name of the cheat. Confirm the name of the cheat and enter the following Action Replay code: 52247d8c 582000c0 12247d8a 00004801 02247d8c e0021c39 02247d90 00000182 d2000000 00000000.
Return to the Action Replay main menu and select "Start" to start "Pokemon HeartGold" or "Pokemon SoulSilver" with the Deoxys cheat enabled. Go to your PC in-game, and you will find Deoxys.