Things You'll Need
Instructions
Pokemon Red and Blue
Start a game and name your character so that the third letter of his name is an "A," "B," "C," "M," O," "P" or "V."
Open your bag and position the items so the item you want to duplicate is located in the sixth slot from the top.
Place a Pokemon with the Fly ability, such as Pidgey or Zapados, and a Pokemon with the Surf ability, such as Squirtle or Psyduck, in your party.
Go to Viridian City and speak with the man who is located directly north of the city entrance. Ask him to show you how to catch a Pokemon. Use your Pokemon's Fly ability and go to Cinnabar Island. Head east and use ̶0;Surf̶1; to move up and down the coast until you enter a battle with Missingno.
Defeat Missingno or flee and open your bag. You will have 128 of the sixth item in your bag. Repeat with other items to max out your supplies.
Pokemon Silver and Gold
Save your game.
Equip the item you want to duplicate onto a Pokemon. Travel to any Pokemon Center and access the PC.
Deposit the Pokemon into a box.
Select ̶0;Switch Box.̶1; Wait for the game to say, ̶0;Saving, do not turn off the power.̶1; Shut off your Game Boy when this appears.
Turn on your Game Boy and reload your saved game. Your deposited Pokemon will be back in your party with his item while a duplicate item and Pokemon will be in the box.
Pokemon Diamond and Pearl
Give the item you want to duplicate to one of your Pokemon to hold.
Engage in a double battle and send out a Ditto and the Pokemon holding the item.
Use Ditto's ̶0;Transform̶1; on your other Pokemon. The Ditto will mimic your Pokemon, including the item it was holding.
Switch out the original Pokemon with one that has the ̶0;Thief̶1; ability, such as Mightyena or Kecleon. Use ̶0;Thief̶1; on the Ditto to steal his item.
Finish the battle and your Thief Pokemon will have the duplicate item.