Updating Firmware
To ensure the codes work properly, install the latest Action Replay Code Manager and firmware. Your Action Replay came with a CD-ROM containing the Code Manager software. Install the software and open it. Click "Software Upgrade" near the top-right corner of the window to ensure the software is up-to-date. Click it again to download the newest Action Replay firmware for your Nintendo DS. Insert your Action Replay into your DS and turn it on. Select "Update Mode" from the Home screen. Connect the cheating device to your PC with the supplied USB cable. Once connected, drag the new firmware download to the PC software's white bar, near the top of the window. The firmware will update after asking you to confirm the upgrade. When instructed, reset your DS.
Adding Codes Manually
Browse the PC software's "Nintendo DS" section to see if "Pokémon Diamond" is already listed. If so, open it. If not, click the main menu's star icon to pull up "Add New Game." Enter the game's name and input "ADAE-636791c0" as the "Game ID." Select "Pokémon Diamond" from the list of available games and select "Add New Code" and the pencil. Enter the code in the text box, copying and pasting makes entering long codes easier. Select "Next" to save the code. Now that they're part of your "Pokémon Diamond" code list, activate them as you would any other Action Replay DS code.
Get the Member's Card
Enter the code "94000130 FCFF0000 B21C4D28 00000000 B0000004 00000000 0000AA3C EDB88320 2000AA68 00000008 D2000000 00000000" into your Action Replay's Code Manager software. Once you're in-game, press the DS buttons "L" and "R" simultaneously to activate the cheat. Enter any PokéMart and talk to the man in green to get the Member's Card. Go to Canalave City and enter the house near the docked boat. Talk to the sick boy, then exit the house and talk to the sailor. He'll take you to Full Moon Island. Walk down the path to find Cresselia and get the Lunar Wing. Go back to Canalave and talk to the boy again to heal him. Go to Harbor Inn in the same city and you'll transport to New Moon Island. Here, you'll find Darkrai in the forest and have the chance to catch him.
Wild Pokemon Modifier
Enter the code "94000130 FDFF0000 B21C4D28 00000000 B0000004 00000000 94000130 FEFF0000 00000890 01ED0001 D0000000 00000000 DA000000 00000892 DC000000 00024620 C0000000 0000000B D7000000 00000000 DC000000 00000006 D2000000 00000000" into your Action Replay's PC Code Manager. Remember, copying and pasting makes entering long codes easier and ensures accuracy. Upon starting your game, press "L" and "R" and you'll find 493 Master Balls in your Items Bag. You want to get rid of some until you have the number of Master Balls that corresponds with the Pokémon's Pokédex number. Darkrai is number 491, so get rid of two Master Balls. Exit the bag and press "L." Head to any patch of grass and walk around until you experience a wild Pokémon encounter, it will be Darkrai. Use one of your remaining Master Balls to catch him. After catching him, throw away the remaining Master Balls, then press "L" again so you don't continually encounter Darkrai.