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Item stack duplication glitch
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Miscellaneous glitches of Pokémon Red and Blue and Pokémon Yellow

Amazing Man (Red and Blue only)| Cable Club escape glitch | Celadon looping map trick | Champion Blue music muting glitch | Coastal Flooding | Cooltrainer move | Cycling based glitch maps | Escape sprite handling glitch | Evolve without an evolutionary stone (Red and Blue only) | Evolving Raichu (Red and Blue only) | Expanded item pack | Expanded Pokédex | Focus Energy glitch | Get stuck in a wall | Ghost Bicycle glitch | Glitch encounter system | Glitch City RAM Manipulation | Infinite Blaine Door | Introduction Nidorino glitch (Red and Blue only) | Invisible PCs (Red and Blue only) | Invisible tree glitch | Item stack duplication glitch | Mute the music in the Pokémon League | Partial trapping move link battle glitch | Pokémon Tower Pokédex glitch | PP Reset Glitch | Recovery move glitch | Rival's effect | See a Ghost without a Silph Scope | Selfdestruct and Substitute glitch | Silph Co. PC Glitch | Slot machine glitch | Stand on a tree | Statue behavior glitch (Red and Blue only) | Substitute glitch | Super effective move AI flaw (Red and Blue only) | Super Glitch | Surf down glitch | Swift miss glitch | Transform assumption glitch | Transform into a Ditto | Trick Zone | Vending machine purchase glitch | Walk around with only fainted Pokémon (Red and Blue only) | Walking lag glitch | Walk on water through Surf | Walking Pikachu happiness glitch (Yellow only) | Wild appeared! | ZZAZZ Glitch

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The item stack duplication glitch is a glitch in Pokémon Red, Blue, Yellow. It can be used to set up an expanded items pack via tricks known as "item underflow" and "dry underflow".

It allows the player to duplicate an item stack with 255 items (so that the player obtains another copy of that item x255) of any item to be held.

It is not to be confused with an item duplication glitch caused by encountering a Pokémon with an invalid Pokédex number, such as Missingno. and 'M (00)'s addition of 128 to the sixth item if there is less than 128 items there.


1) 255 of an item in a slot below the first item are needed.

In Pokémon Red and Blue, this is possible by using the old man glitch to encounter a Missingno. or 'M (00) with an item in the sixth position that has a quantity less than 128.

From there, if the player originally had one of the item, they can use the item in battle to get 127 and capture Missingno. or 'M (00) to get 255 items in the sixth position. Alternatively, the player can end the battle, then toss one of the item (or whatever number needs to be tossed to get less than 128) to get 127 items in the sixth position, and then encounter another Missingno. or 'M (00).

In Pokémon Yellow, the player can still do this trick with a Yellow regular Missingno. encountered with the Ditto Trick, but a freeze is likely. It is more ideal to use a Kabutops Fossil (Special 182), a Aerodactyl Fossil (Special 183) or Pokémon Tower Ghost (Special 184) Missingno., which never freeze the game or cause any known side effects after being sent out from the opponent's side (though if the player sends one out then its backsprite will corrupt the Hall of Fame) other than duplicating the player's sixth item.

In Pokémon Red, Blue, Yellow, the level 127 Missingno. variant of the TMTRAINER effect can be used to duplicate the player's sixth item if they catch it, but pulling this off may not work after a certain point in the player's game, so more reliably, but more slowly, the Cable Club escape glitch can be used in Red, Blue, Yellow to battle a Trainer with more than one Fossil or Ghost Missingno if the other player that 'player one' linked to had them.

The Cable Club escape glitch can also be used to encounter Missingno. This may be ideal in Pokémon Yellow if the player does not have the required Special stat for encountering a (Fossil or Ghost) Missingno. with the Ditto Trick, or if the level 127 Missingno. variant of the TMTRAINER effect is not working.

2) An item which is unimportant to the player in the slot directly below the item that the player has 255 of. This will be replaced with the item stack above it.


  1. Toss all of an item above the stack of 255 items.
  2. A copy of the stack of 255 items will appear above it. The player's number of items is decreased by 1, and items before and including the Cancel button are not shifted up, the item above the Cancel will act like Cancel.

The player's last item will become unusable, so it is ideal to use an item there that is not valuable (key items may be lost). This item can be deposited in the PC as PC items are not affected by the item stack duplication glitch.


This glitch can be used to make regular items function as Cancel, because the location of the Cancel button is not shifted up.

At memory address D31D (D31C in Yellow), the player's current number of items is stored. If the player had, say 09 items, the item at position 10 is selectable but not usable. Normally the Cancel button is always at [number of current items +1].

When the player tosses a stack of items above the stack of 255 items, although the player's number of items is decreased by 1, the items below it are not shifted up. Consider this example:

Before tossing the item:

Number of items: 09

  1. Master Ball x1
  2. Ultra Ball x255
  3. X Accuracy x96
  4. Hyper Potion x6
  5. X Attack x66
  6. Full Restore x2
  7. Full Heal x98
  8. Max Revive x5
  9. Poké Ball x1
  10. Cancel

After tossing the item:

Number of items: 08

  1. Ultra Ball x255
  2. Ultra Ball x255
  3. X Accuracy x96
  4. Hyper Potion x6
  5. X Attack x66
  6. Full Restore x2
  7. Full Heal x98
  8. Max Revive x5
  9. Poké Ball x1
  10. Cancel

Note that the Poké Ball x1 is at position 09, which is the player's new number of items +1, so the Poké Ball x1 is selectable but not usable, just like how Cancel is supposed to work.

Incidentally, if the Cancel button was usable (e.g. if it was at position 9 to begin with), it would act like TM55.

Buying an item (or otherwise adding an item to the player's inventory) will erase the item acting as the Cancel button as well as those underneath it. A normally functioning Cancel button will be directly below the bought item. This way, it is possible to erase unwanted key items and hard to toss glitch items.


  1. Faster duplication of items than encountering Missingno.
  2. Erasing unwanted key items and hard to toss glitch items.
  3. Item underflow glitch