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99 item stack glitch
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Major glitches of the Pokémon series

Arbitrary code execution (template, remote, cart-swap, unintended ROM code execution) | 2x2 block encounter glitches (Left-facing shore tile glitch (in-game trade shore encounter trick, old man trick, Trade link up shore encounter trick, Fight Safari Zone Pokémon trick)) | 99 item stack glitch | Bad clone glitch (????? party overloading (Type 0xD0 move glitch, ????? map corruption, | Celebi trick, Celebi Egg trick, Shiny Celebi trick, glitch move map corruption, overloaded party map corruption, Glitch Unown (Glitch Unown map corruption) Duplicate key items glitch (infinite items and item creation, expanded Balls pocket (TM/HMs outside of the TM/HM pocket, Glitch Pokédex categories)) | Berry glitch | Bug-Catching Contest data copy glitch (Japan only) | Cloning | Ditto DV manipulation | Elite Four door glitch (Japan only) | Expanded party encounter table manipulation | Generation IV item cloning glitch (Japan only) | Glitch City (Safari Zone exit glitch, RAM manipulation) | Glitch meta-map script activation (Generation I) | Infinite Master Balls (Colosseum) | Large storage box byte shift glitch (storage box remaining HP glitch, maximum stat glitch) | Item duplication glitch | Item stack duplication glitch (Generation I expanded items pack (Glitch Rocket HQ maps, Map FE (English and non-English European Yellow), Map script pointer manipulation (arbitrary code execution, map script pointer item ball manipulation), Text pointer manipulation (arbitrary code execution, item ball manipulation, mart buffer overflow), Trainerless instant encounter glitch) | Mimic glitch (Japan only) | Out of bounds Glitch City (Generation II) (Slowpoke Well out of bounds corruption (French version)) Lumiose City save glitch | Pikachu off-screen glitch (Trainer corruption glitch) | Pokémon merge glitch | Pomeg glitch (Pomeg data corruption glitch) | Roaming Pokémon encounter glitch | (Mimic) Transform Rage glitch | Select glitches (Japan only) (Closed menu: Dokokashira door glitch (international), Fossil conversion glitch (international), Second type glitch, Skip to Level 100 glitch, Trainer mutation glitch, walk through walls (international) Special menu: Lift glitch, Badge describer glitch) | Sketch glitch | SRAM glitch (Generation I) (255 Pokémon glitch, send party Pokémon to a new game) | Surf down glitch (Grass/rock Surfing glitch (Spanish/Italian only) (English)) | Time Capsule exploit | SRAM glitches (Generation II) (Mailbox glitches, Mystery Gift item corruption, Trainer House glitches) | Tweaking | Trainer escape glitch (Death-warp, Mew Trick, Ditto Trick, Experience underflow glitch) | Buffer overflow techniques (Japanese unterminated name glitch item instant encounter glitch, LOL glitch, Rival LOL glitch, Instant LOL glitch, RAM LOL glitch, oobLG, blockoobLG, Instant encounter infinite chain glitch (LGFly)), Super Glitch (Generation I) (party remaining HP glitch), Super Glitch (Generation III), Text pointer manipulation mart buffer overflow glitch, CoolTrainer♀-type move, Double distort CoolTrainer♀ corruption, Yami Shop glitch) | Walk through walls (ledge method, museum guy method, Rival's effect, Select glitch method (international), Brock Through Walls) | ZZAZZ glitch (party Pokémon box data shift glitch)

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Corrupting the screen palette after purchasing Ultra Balls.

The 99 item stack glitch is a memory corruption glitch and natural glitch which occurs in Pokémon Red and Blue and Pokémon Yellow (Japanese). It does not work in English Yellow.


If the player performs a task which adds to the number of items in a list (purchasing an item from a Poké Mart, depositing it via the PC or withdrawing it via the PC) while they have an existing stack of that item ×99 in the last slot of the inventory (e.g. Ultra Ball ×99), the game will try to add to an item quantity of the same item from beyond that slot in an attempt to contain the items in an existing stack without creating a new one.

Due to a glitch, the end terminator is ignored if it directly proceeds an item quantity, and the game may add to the quantities of items even if the 'item quantity' represents an unrelated memory address.

The glitch won't happen if the player has less item slots occupied than previously (eg, if the player has had 15 item slots filled in his inventory, having less than 15 item slots occupied will prevent the glitch.

Note that any memory address with value hex:FF will end the search ; hence having all 8 badges will prevent most corruptions.


  • In English versions, when buying Ultra Balls with Ultra Ball ×99 in the last slot of the inventory, it is possible to corrupt $D35D (item 32 quantity; controlling the screen palette) if $D35C (item 32; current sound bank value) is 2 (Ultra Ball).
  • In English versions, one can exploit the Yami Shop glitch to buy Master Balls. If D364 (Block-X ID) is 01 and there are no Master Ball stacks which aren't ×99 before it, then one can add to D365 (map exit warp) to access locations up to hex:63 (S.S. Anne Deck). It may be necessary to change the quantity in address D358 to 99 first.
  • In Japanese versions, when buying Great Balls with Great Ball ×99 in the last slot of the inventory, it is possible to corrupt number of badges ($D2D5) if the options byte is equal to 3 (Battle Animation On, Battle Style On, medium text speed).

External links

YouTube video by TheZZAZZGlitch
YouTube video by ChickasaurusGL
YouTube video by SM

(warp to S.S. Anne exploit)

YouTube video by ChickasaurusGL

(in Japanese Blue)

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