Back in the day when Ruby and Sapphire were still new, it was proven that you could not clone Pokémon as you could in Gold, Silver, and Crystal. However, it recently surfaced, thanks to a person named Poketaz (albeit a Serebii.net member, so that site's eaten its lunch), that it is now possible to clone in Emerald.
- Go to the Battle Tower in the Battle Frontier. Go to the PC and save your progress.
- Deposit the Pokémon you wish to clone in an empty box by selecting Deposit Pokémon.
- Log out and save again. Now access the PC again and withdraw the Pokémon you deposited.
- Without saving, go over to the attendant hosting the Link Multi Battle tournament (the one farthest right). Confirm that you want to challenge and select your two Pokémon.
- When the attendant says she needs to save the game, respond 'Yes'. The game will freeze for two seconds. Once the game starts running again, turn off your Game Boy Advance and then turn it on again. Do NOT save the game at this point.
- The Pokémon you deposited and withdrew will appear in both your party and the PC.