IMPORTANT: Be sure to follow the instructions carefully, as this code can crash your game if you do it wrong.
1. Go to your PC and select "Move Pokemon".
2. Make sure the Pokemon you want to clone is in a box with at least 1 free space.
3. Select the Pokemon. A menu will pop up, the first option being "Move".
4. Press Start, Select and A at the same time.
5. Press L and R at the same time. This will take you to the box right before the one you are cloning in, and it will refresh the cloning box. DO NOT SKIP THIS STEP! IF YOU DO, YOUR GAME WILL CRASH.
6. Be sure not to put down the Pokemon, and go back to your cloning box. The Pokemon should now be cloned: one of them, the one you have selected, and the other one in the box.
7. Enjoy your cloned Pokemon! :)