Things You'll Need
Instructions
Insert Pokemon Diamond or Pearl into your Action Replay DS cartridge and place them into your Nintendo DS game slot. Check both cartridges for looseness before turning on your Nintendo DS. Tap the "star" icon after the Action Replay software boots. Choose the name of your game from the game list, tapping the "pencil" icon to continue.
Add your Action Replay codes to the game list after checking both game name and ID. Type in the Action Replay code "94000130 FCFF0000 B21C4D28 00000000 B0000004 00000000 10001170 00000098 D2000000 00000000" for Chikorita. The code "94000130 FCFF0000 B21C4D28 00000000 B0000004 00000000 10001170 0000009B D2000000 00000000" works for Cyndaquil, while "94000130 FCFF0000 B21C4D28 00000000 B0000004 00000000 10001170 0000009E D2000000 00000000" works for Totodile. Save your codes and tap the "Start" button to boot your game.
Go to "Oreburgh City" after your game resumes, heading to the "Oreburgh Museum" on the city's northwest side. Hold down the "L" and "R" buttons to activate the code before going into the museum. Walk to the desk inside to talk to a scientist, who will give you a Level 20 version of your Johto starter of choice.