Item duplication glitch: Difference between revisions

The item duplication glitch may refer to one of two known glitches that duplicate the items in a player's bag. Both glitches are only found in Generation I.

Missingno. item duplication glitch

The Missingno. item duplication glitch (known in some circles as the Rare Candy glitch due to the preferred item chosen to duplicate) is an infamous glitch in Pokémon Red and Blue. It allows the player to duplicate items in his bag.

Through the development of Pokémon Yellow, which occurred in the two years following the release of Pokémon Red and Green in Japan, the Old man glitch was disabled by blanking the data for wild Pokémon before overwriting it, and reprogramming shore tiles to act as water tiles, thus removing this glitch too.

Mechanics

Results

The sixth item in the bag is duplicated. The quantity of this item will be increased by 128 (for defeating or running) or 255 (for catching, although catching these can trigger other glitchy effects). After using all duplicated items and then repeating the glitch, an infinite amount of items can be obtained. Key items can be duplicated, but the only key items which are practical to duplicate are the Dome Fossil, Helix Fossil and Old Amber.

Cause

Every Pokémon has a "Pokédex byte" that tells the game whether it has been seen or caught. A value of 0 means the Pokémon hasn't been seen or caught, 128 means it's been seen, and 255 means it's been caught.

Missingno.'s Pokédex byte is in the same location as the byte that stores how many of the 6th item is in the bag, as well as 'M's. This is why, when Missingno. or 'M is encountered, the sixth item slot is increased by 128 (or 255 if it is captured). The glitchy box symbol is a result of the game attempting to display a number greater than 99, which causes it to grab sprites from beyond the number sprites. Sometimes it can appear to be a blank tile, but if one goes somewhere else or out of battle it will revert back to an unusual tile.

A way to tell whether " 9" is in fact 9 or [blank tile]9 is to select Toss. The quantity is displayed with a leading zero if the amount is actually 9, and as simply " 9" if not.

Performing the glitch

The player must perform the Old man glitch to encounter Missingno. or 'M, then defeat, run from, or catch the Missingno. or 'M.

After the battle, open the menu and view the items currently in the bag. If done correctly, the game should show a glitch character followed by a standard number. This glitch character represents a place value of 10 or above.

Note that if the amount of the item in question is already 128 or more, this glitch will not work.

255 stack duplication glitch

The 255 stack item duplication glitch is caused by obtaining 255 of an item, and then tossing an item above it. This creates another stack of 255 items.

Performing the glitch

The player must obtain 255 of an item. The only way to do this is via the Missingno. item duplication glitch. As long as there is exactly 255 of an item, tossing an item above it will cause this glitch. It means that the stack of 255 items is copied to the slot above it, as well as its original slot. Tossing an item below the 255 stack causes no glitch. Swapping the places of two items causes no glitch. When there are two or more non-adjacent item piles of quantity x255, only the x255 pile closest after the tossed item duplicates.

Using the glitch once will make the last item in your inventory act as the Cancel button. Twice will make the second to last item in your inventory act as the Cancel button. And so on. You cannot scroll beyond the Cancel button, even though the scroll arrow is there. Items below the acting Cancel button will be unreachable. The acting Cancel button can be swapped with another item, which will act as the Cancel button.

Adding an item to your bag will erase the item acting as the Cancel button as well as those underneath it (not like you could reach those anyway). A normally functioning Cancel button will be directly below the bought item.

Aside from the Cancel button issue, all items will function normally.

How it works

When an item is tossed, each item below it is copied upward one space, starting with the item directly below the tossed item and going down. However, when the game encounters a pile of quantity x255 while going down the list, it is copied up, but the items after it are not, leaving two adjacent piles of x255 of the same item. The game still decreases its count of the total number of inventory items by one (which accounts for the messed up Cancel button).

When the game goes down the list on this copying spree, encountering an FF byte signals "Cancel button! Stop copying after this!" even though in this case the FF byte is for item quantity, not item type. Under normal cases, nobody would have x255 of an item anyway. Under normal cases, since the Cancel button masks anything after it, the game doesn't have to delete the extra Cancel button left behind after copying the cancel button up one space.

Source

• Glitch City Laboratories Forums

This article is part of Project GlitchDex, a Bulbapedia project that aims to write comprehensive articles on glitches in the Pokémon games.