Styleswitcher-

Emerald Cloning Glitch

All generations of Pokemon have had a cloning glitch, but this is the easiest and most non-hazardous one around. With Diamond and Pearl however, this glitch gained an extra use: Since Pokemon are transferable to Diamond and Pearl but cannot be brought back, why not clone them so you can have the Pokemon in both games? Anyway, here's how you do it:

Go to the Battle Tower (located in the Battle Frontier) and deposit the Pokemon you want to clone in the PC.
Save the game.
Withdraw the Pokemon that was deposited, don't deposit another Pokemon though because it will be lost if you do.
Start entering a battle in the station next to the PC. Agree to saving your game, then there will be a short pause.
After the pause, the lady will ask if you want to overwrite your current save file. Don't answer, but turn the game off.
When you turn the game on, you will have two identical copies of the Pokemon-one in your party in one in your PC. Also, any item the Pokemon was holding will also be cloned.

If you follow all the steps correctly, nothing bad will happen to the game. But first, try it with a weak Pokemon just to make sure you know the steps. It is rumored that this glitch will not work with Rayquaza and Kyogre, but anyone who wants to try it can tell me what happened. Now how does this work? I'll explain it to you: When you save the game, every aspect of the game is saved, including your box. But that short pause after agreeing to save does more than you think- it saves your party and your current position, but not your PC box. So when your game is restarted, the game has two locations of the Pokemon saved, your PC box and party. Have fun cloning!