Things You'll Need
Instructions
Drop off up to two low-level Pokemon at a day care center. There are multiple day cares located throughout the game world, though the easiest one to use for this process is in Solaceon Town in Eastern Sinnoh.
Travel to Floaroma Town on the western edge of Sinnoh and locate the Fuego Ironworks. You will need to surf on a water Pokemon off the left side of the bridge east of the town. The waterway leads straight to the Ironworks.
Enter the Ironworks and go left. You will hit a plate on the floor that will send you spinning off through the room. As you hit other plates, you will continue to spin farther into the Ironworks.
Spin through the works until your character stops on its own. You will find yourself between a wall and a spin plate. Hold down the left arrow button and the "B" button on your Game Boy Advance and your character will step onto the spin plate, spin backwars, then step on again in an endless cycle.
Place two heavy objects on the two buttons to hold them down. Use rubber bands to hold the items in place so they don't shift. Your character will now continue to spin as long as the Game Boy stays on. Your Pokemon will constantly gain levels while you go about your business or go to sleep.
Plug your Game Boy Advance's charger cable in and connect it to a power source to ensure it stays on as long as you want it to.
After hours have passed, remove the heavy objects and return to the Pokemon day care. Retrieve your Pokemon, who will be as much as 40 levels higher after a night of training.