From the game Pokemon Gold/Silver/Crystal for the Game Boy
You can clone a Pokemon by depositing it and then changing boxes. While changing boxes, shut the game off when it says "saving, do not turn off the power". When you turn the game back on, the Pokemon will still be in your party, but there will also be one in the pc! If you withdraw anything before attempting this, save the game first, otherwise whatever you withdrew will be erased, even if it is a Pokemon! You can duplicate items by having a Pokemon hold it and then cloning him! But, save the game after you attach the item to the Pokemon and before you do the glitch, or it won't work.
Submitted by: lazio62