Duplicate key items glitch

Miscellaneous glitches of Pokémon Gold and Silver and Pokémon Crystal

Battle transition oversight | Change player color glitch (Crystal only) | Daylight Saving Time exploit | Get all three starters (Generation II) | Glitch Unown | Glitch dolls | Horn Drill and Fissure glitch | Unused and redundant Egg moves

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This Duplicate Key Items glitch is a glitch in Pokémon Gold, Silver and Crystal that allows byte shifting in the item pack, and using a more precise setup, the Balls pocket to contain more than the maximum amount of items.

Requirements

• Two Pokémon Gold, Silver and Crystal games on two different Game Boys
• A link cable
• Access to the Cable Club on both games
• Machine Parts and SecretPotion on both games

Performing the glitch

1. Give the Machine Parts to a Pokémon
2. Trade it to the other game
3. Take the Machine Parts off the traded Pokémon
4. Repeat with the SecretPotion (you can use the same Pokémon as before)
5. On the game with two SecretPotions and two Machine Parts
6. Put both Machine Parts in the last two slots of the Key Items pocket
7. Swap both items, which will turn into a single slot
8. Remove the Cancel item
9. Put both SecretPotions in the last two slots of the Key Items pocket
10. Swap these, and all bytes up to the Cancel in the Balls pocket will be shifted upwards

Expanded Balls pocket

If the item ID of the first ball in the Ball pocket will be written into the item counter, meaning that a Fast Ball (hex:A1) will give 161 items in the Balls pocket (which is far beyond the normal limit)

Arbitrary code execution in Pokémon Crystal

Celebi obtained through this trick

Requirements

• Two Game Boys
• A Pokémon Red and Blue or Pokémon Yellow game
• A Pokémon Gold and Silver or Pokémon Crystal game
• Another Pokémon Crystal game, that has a TM33 in the first PC item slot
• A link cable
• Access on all games to a Cable Club

Performing the glitch

1. Use 8F (Pokémon Red and Blue) or ws m (Pokémon Yellow) to obtain a Pokémon with the following nickname : (any character)x2, hex:C3, hex:F2, hex:D8, then whatever you want
2. Trade it to one of the Gen II games
3. On the other, perform the Expanded Balls pocket glitch