Things You'll Need
Instructions
Connect the Action Replay to your computer via a USB cable. Launch the "Action Replay DS" software, if it doesn't open automatically.
Scroll through the list of games in the "Subscriptions" pane. Drag "Pokemon Diamond" into the "My Codelists" pane. Click the "Custom Codelist" button.
Right-click "Pokemon Diamond," and select "Add New Cheat." In the cheat name box, type "Magby."
Enter "94000130 fffb0000" and "d5000000 000000f0" on the first and second lines of the code box. Next, enter "b21c4d28 00000000," "b0000004 00000000" and
"c0000000 0000000b."
Type "d7000000 00024620," "dc000000 00000006" and "d2000000 00000000" on the final three lines. Click "OK."
Remove the Action Replay from the computer, and connect it to the Nintendo DS. Start "Pokemon Diamond as usual. When you load the game, enter an area where wild Pokemon roam, like tall grass. Hold "Select." A Magby appears, which you're able to fight and capture.