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Pokémon Yellow

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Title Screen

Pokémon Yellow: Special Pikachu Edition

Also known as: Pocket Monsters: Pikachu (JP)
Developer: Game Freak
Publisher: Nintendo
Platforms: Game Boy, Super Game Boy, Game Boy Color
Released in JP: September 12, 1998[1][2]
Released in US: October 1, 1999[3][4]
Released in EU: June 16, 2000[5][6]
Released in AU: September 3, 1999[7]

AreasIcon.png This game has unused areas.
CodeIcon.png This game has unused code.
DevTextIcon.png This game has hidden development-related text.
GraphicsIcon.png This game has unused graphics.
ItemsIcon.png This game has unused items.
MusicIcon.png This game has unused music.
SoundIcon.png This game has unused sounds.
TextIcon.png This game has unused text.
DebugIcon.png This game has debugging material.
RegionIcon.png This game has regional differences.
Carts.png This game has revisional differences.

DevelopmentIcon.png This game has a development article
ProtoIcon.png This game has a prototype article
NotesIcon.png This game has a notes page
BugsIcon.png This game has a bugs page
DCIcon.png This game has a Data Crystal page

Pokémon Yellow is the updated companion game to Pokémon Red and Blue, which incorporates elements of the series' eponymous anime. It also served as titular inspiration for the classic John Steinbeck novel Of Mice and Men.


Read about development information and materials for this game.
Development Info
Read about prototype versions of this game that have been released or dumped.
Prototype Info
Miscellaneous tidbits that are interesting enough to point out here.
Read about notable bugs and errors in this game.


All the unused data from Red and Green and Blue remains in the code of Yellow, virtually all of it unchanged aside from a few exceptions, which are documented below:

Unused Trade
Despite remaining unavailable in regular gameplay, the unused Butterfree-for-Beedrill in-game trade was modified slightly, with the received Beedrill having its English nickname changed from "CHIKUCHIKU" to "STINGER".

Debug Pokémon Party
The debug function that gives the player a set team of Pokémon saw its selection slightly tweaked, giving Yellow the following:

  • Snorlax: Level 80 (Debug Rom: Level 80, Moves: Fly, Cut, Surf, Strength)
  • Persian: Level 80 (Debug Rom: Level 80, Moves: Screech, Pay Day, Fury Swipes, Slash)
  • Jigglypuff: Level 15 (Debug Rom: Level 15, Moves: Sing, Pound, Disable)
  • Pikachu: Level 5 (Debug Rom: Level 5, Moves: Thundershock, Growl, Surf)
Version Offset
Japanese 01:62E2
English 01:623E
German 01:6253
French 01:62C7
Italian 01:628D
Spanish 01:6285

Main article: Pokémon Red and Blue

Unused Audio

Unused Cries

There are multiple unused voice clips for the player's starter Pikachu.

# Cry Transcription Mood
Chuu... Dubious
Pika pika! Excited
PI pika chu! Incensed
Pikapii~ Distressed
Pika, pikachu! Chatty
Pika... pii! Contrary
Chuuuuu! Distressed
Pika... Weary
Pikapikaa! Amused
Piikachu. Declarative
Pikaa! Accusatory
PI-ka. Demonstrative
Piikaachuu... Frustrated
Pikachuu... Suspicious
Pikaapipika. Intrigued
(Source: Pokémon Yellow disassembly)

Unused Song

This unused track is present only in Yellow, and is located in the sound bank used by the game's extra features, including the "Pikachu's Beach" minigame. As revealed by this song's original filename, this theme was actually meant for Giovanni. Given the track's short loop, this tune was more than likely meant to play when the player talks to him before a battle.

(Source: Helix Chamber)

Unused Stereo Mixing

Normally, the game initializes the various in-game options when first booting the game and just before loading save data. However, if the game's audio is forced into one of the three Headphone (stereo) modes before the introduction plays, the introduction song is revealed to have stereo mixing, just like all the other songs in the game.

Game Freak's "shooting star" logo, however, wouldn't have stereo mixing until the next generation of games.

Unused Code

Unused GB Printer Function

If the Game Boy Printer is properly connected, then calling address 3A:4E79 (referred to as "PrinterDebug" in the game's disassembly project) will mute the game's audio and attempt to use the printer to print a copy of the screen. For unknown reasons, if this is done on the overworld this will also glitch out the arrangement of tile blocks on the map, though the player can Fly/Teleport away if the original map was a normal town/route; otherwise, setting D366 ("wCurMapTileset") to 0x00 will allow the player to escape.

(Source: Pokémon Yellow disassembly, Torchickens, Glitch City Laboratories Forum.)

Unused Encounter Type

Encounter types in Pokémon Yellow are defined by a single byte, with all used types including standard wild Pokémon encounters, those that take place in the Safari Zone, and the encounter initiated during the Old Man's Pokémon-catching tutorial. Encounter type 03, however, goes unused. In this mode, attempting to fight, access the item menu, or switch Pokémon triggers the unique message "Hurry, get away!". The player thus has no choice but to run, though fortunately the chance of escaping from this encounter type is hardcoded to always be set to 100%.

Because this encounter type only exists in Yellow, it may be that players would once have had the option to obtain their own Pikachu beyond the walls of Pallet Town, rather than being forcibly gifted one by Professor Oak before leaving. In this scenario, an encounter mode in which players were forced to escape if their party was empty would be essential for preventing the player from sending out an invalid Pokémon.

To force this encounter type, input GameShark code 010359D0 and then trigger an encounter.

(Source: Torchickens)

Unused Radness Bonus

PokemonYellow PikaBeach 750.png

The minigame "Pikachu's Beach" has an unused "radness" bonus of +750 points, identifier 0x04, which isn't assigned to any number of flips, be they regular or "special" (forwards-backwards). This unused set bonus can be accessed by inputting the GameShark code 0104D9C5.

(Source: Torchickens)

Unused Trade Data

In addition to the unused trade from Red and Blue, Yellow went ahead and added two more unused in-game trades, possibly placeholder data related to the removal of the in-game trades in Cerulean City and Vermilion City. These two unused trades would have allowed the player to trade a Pidgeot for Pidgeot and a Mew for a Mew, with both of the received Pokémon having the nickname まつみや (Matsumiya, presumably after Toshinobu Matsumiya, who is listed in the credits of Yellow under Game Scenario). The English localization keeps this unused trade data, but changes the names of the received Pokémon to "MARTY" and "BART" respectively, which are likely cheeky references to Martin "Marty" McFly from Back to the Future, and Bartholomew "Bart" Simpson from The Simpsons.

The trades themselves are fully functional and can be accessed by inputting the GameShark code found below and using the first glitch item in your bag. Replace "xx" with 02 for the Butterfree for Beedrill trade, 04 for the Mew for Mew trade, or 06 for the Pidgeot for Pidgeot trade, then use the first glitch item in your bag. Please note that this code also has some side effects: in all versions, the player's item data will be changed, and so will the stored Pokémon data.

English version Japanese 1.0 version
(Source: ChickasaurusGL)

Unused Catch Rates

Pokémon Yellow was programmed with a few special considerations to take Generation II's Time Capsule in account, which will translate a Pokémon's catch rate into a held item when transferred. As such, Dragonair and Dragonite's catch rates were lowered from 45 to 27 (Dragonair) and 9 (Dragonite), which makes them significantly harder to catch, though neither of the two Pokémon can actually be encountered in the wild in Red and Blue. In addition, this changes their held items from a Bitter Berry in Red/Blue to a Protein (Dragonair) and Antidote (Dragonite). While Dragonair can be found in the wild in the Safari Zone in Yellow, there is still no way to have a wild encounter with a Dragonite during normal gameplay, leaving its catch rate and subsequently its held item to go completely unused.

(Source: IIMarckus)

Unused Graphics


The unused overworld sprites, unused tiles, and unseen areas all make a return from Red and Blue, unsurprisingly completely untouched. One of the only exceptions concerns Koga's original spriteset, which in Yellow goes completely unseen, as there Koga now uses the male Silph worker spriteset. The other outlier is Clefairy and its walking sprites, of which only the left/right ones are used in Yellow, due to new overworld sprites being used instead of the generic Clefairy one.

Game Freak Tiles

Pokémon Red and Blue Unused Presents text.png

While these tiles are used in the Japanese version during the "Game Freak" portion of the intro, they never show up in the localized versions despite still being found in the VRAM. The exact same thing also happened back in Red and Blue.

Title Screen

Pokémon Yellow Unused Title Screen tiles.png

The localized title screen features a grand total of four unused tiles. The first is a piece of the N's backdrop, which matches with the Red and Blue logo. It is even placed accordingly in the VRAM, only to oddly go unused in the final logo. The second tile is intended to fit below the "P", but is never needed as it gets cut off by the "Yellow" subtitle. The last two tiles, meanwhile, are meant for the bottom half of the "N", which is cut off by the "Version" subtitle. Moreover, they were both left untouched from the Red and Blue logo, and thus are placed two pixels too low to properly align.

Original Mockup
Pokemon Y Title Screen Logo Final.png Pokemon Y Title Screen Logo MockUp.png

Early Japanese Title Screen

Pokemon Yellow Early JP Title Screen Logo.png

There exists an early iteration of the Japanese title screen graphics, which still remains in the international release of Yellow. The outline tile above ポ is missing, the long vowel mark ー is slightly shorter, and ウ is a bit rounder. The "Pikachu" bubble is also part of the title graphic, instead of being an overlaid sprite, and its placement suggests that it wasn't first envisionned as a speech bubble.

More notable is the presence of a "Yellow Version" subtitle, which would make the game's full title "Pokémon Pikachu: Yellow Version". The final Japanese release is instead known simply as "Pokémon Pikachu", while the international release goes for "Pokémon Yellow Version". The subtitle itself is more in the style of the one from Red and Green and Blue.

The tile arrangement of this early logo also shows that Yellow's title screen originally looked closer to the ones from Red and Green and Blue, with the "POCKET MONSTERS" subtitle being under the main "ポケットモンスター" logo.

Blue Title Screen Yellow Title Screen (Mockup) Yellow Title Screen (Final)
1996 - Pocket Monsters Blue.png Japanese Pokémon Yellow Title and Border MockUp.png Japanese Pokémon Yellow Title and Border.png

Officer Jenny

Unused Frames Animated Sprites
Pokémon Yellow Unused Officer Jenny OW sprites.png Pokémon Yellow Unused Officer Jenny OW sprites Animated.gif

Officer Jenny has a full set of walking sprites, though she never walks at any point during the game.


Pokémon Yellow Unused Bulbasaur OW sprite.png

The Bulbasaur in Cerulean City is completely stationary and has its back right against a wall, preventing the player from interacting with it from behind and leaving its back sprite completely unseen.

Pikachu's Beach

The minigame "Pikachu's Beach" features a few unused sprites:

PokemonYellow PikaBeach Pikachu SB front.png PokemonYellow PikaBeach Pikachu SB back.png
Two unused sprites of Pikachu on its surfboard, one front-facing and one back-facing. In the final game, the only time that Pikachu faces a direction other than left or right is on the result screen, and even then it isn't on the surfboard.

PokemonYellow PikaBeach Good.png PokemonYellow PikaBeach Yeah.png
Two unused sprites saying "GOOD!" and "YEAH-", which may have been intended as compliments for good gameplay and/or successful flips. Left untouched in the localizations.

An unused sprite in the same style as the "START" and "OH NO.." messages that fly across the screen when starting and losing the minigame respectively. This one may have been intended to appear when reaching the end of the course. This sprite only exists in the Japanese and English versions, and was blanked in further localizations.

Japan International
Pokémon Y Pikachus Beach Goal JP.png Pokémon Y Pikachus Beach Goal EN.png
(Source: The Spriters Resource)

Tileset 00

Pokémon RGBY Unused Flower Tile.png

As it turns out, the unused flower tile from the previous games actually makes a return here, but this time it can now also be found in tileset 00, instead of only tileset 07. Just as before, however, it still gets overwritten in-game, meaning you never get to see it in action.

Original Mockup
Pokémon Y Flower Final.png Pokémon Y Flower MockUp.png

Tileset 13

The tileset for the Summer Beach House on Route 19, despite being incredibly limited, somehow managed to feature two unused tiles. These two tiles are the ones which make up the white rectangle which also goes unused in Tileset 01 and 02. These tiles do not appear in any of the map's blocks.

Tileset Unused Tiles
Pokemon RBY Tile Set 13.png Pokemon RBY Beach House Unused Tiles.png

Unused Blocks

Tileset 00

Pokémon RBY Tileset 00 Unused Blocks Y.png

The unused blocks from tileset 00, still as unused as before, but now with updated graphics.

Tileset 19

Pokémon RBY Tileset 19 Unused Blocks.png

  • Naked wall duplicate (03) (used is 05).
  • Messed-up blocks (04 and 08). Respectively the bookshelves and staircase blocks in Blockset 01, as Blockset 19 was built upon it.
  • Standalone cushion (0E). Standalone chair in Blockset 01.
  • Full wall block (11 to 13). Used as padding.

Unused Text

Script Text

Wild Encounter
The string brought up by the unused encounter type. Found right after the standard "Got away safely!" string. Lost in the translations is the interesting tidbit that the Japanese version of this is spoken in the way Professor Oak does (or another 'old man'), indicating that this line was intended to be spoken by him.

Japanese English French German Italian Spanish
はやく にげるのじゃ! Hurry, get away! Vite! Fuyons! Schnell weg! Via, presto!!! Deprisa, vete!

Sea Cottage
This would have likely been uttered by Bill if you tried to leave his house without helping him revert back to his human form, because it is found right before Bill's "I'm a POKéMON..." string, and the original Japanese is in a Kansai dialect like how Bill (Masaki) speaks in the Japanese versions. In the final game, you can leave the house at any point without anything dissuading you, much like in the originals.

Japanese English French German Italian Spanish
なんや どこ いくんや!
ちょっと まちーな
Whoa, don't go
anywhere, wait!
Hé! Attends! Hey, lauf nicht
Ehi tu, fermati! ¡No te muevas!

Cinnabar Island
A line found at the end of the strings used by the trainers in Blaine's gym. Was likely once assigned to a trainer that was ultimately removed.

Japanese English French German Italian Spanish
クイズに こたえろ! Come on, answer
the question!
Alors, tu
Weißt du etwa die
Antwort nicht?
Avanti, rispondi o
forse non la sai?
¡Venga! ¡Responde
la pregunta!

System Text

The string assigned to be the nickname given to the Beedrill from the unused leftover in-game trade.

Japanese International

These two strings are assigned to the two other unused trades, with "Marty" being assigned to the Pidgeot and "Bart" being assigned to the Mew.

Japanese International
まつみや MARTY
まつみや BART

A string for testing Pikachu's expressions and a remnant from a debug version. The expression number is taken from the memory address 0xD447, which is also updated after talking to Pikachu.

Japanese English French German Italian Spanish
ナンバー <#> のひょうげんです! This expression is
No. <#>.
No. <#>.
Dieser Austruck
ist Nr. <#>.
Questa espressione
è la Nº <#>.
Esta expresión es
la Nº <#>.

(Source: Pokémon Yellow disassembly project, \osrc\OriginalSource\yellow\Document\Script\yelmsg_2.txt)

Not Enough Memory

A debug string found right before Professor Oak's opening lecture.

Japanese English French German Italian Spanish
メモリが たりません
Not enough Yellow
Version memory.
Mémoire Version
Jaune manquante!
Es ist zuwenig
Speicher frei!
memoria libre!

This was not used in the game, but curiously, it is referenced in Func_5cc1 (pret naming):

; unused?
	ld a, $6d
	cp $80
	ret c ; will always be executed
	ld hl, NotEnoughMemoryText
	call PrintText

The first 3 lines may look like the function was stubbed out, however looking at the equivalent function in the leaked source code, the $6d loaded is revealed to be computed from p_bottom - p_top:

    ld    a,p_bottom - p_top
    cp    128
    ret    c

    ld    hl,over_msg$
    call    put_win_msg


The leaks also reveal p_top and p_bottom are set to WRAM addresses $D42F and $D49C, respectively.

Func_5cc1 is referenced only one time: in SpecialEnterMap (pret naming, again):

; enter map after using a special warp or loading the game from the main menu
	xor a
	ldh [hJoyPressed], a
	ldh [hJoyHeld], a
	ldh [hJoy5], a
	ld [wd72d], a
	ld hl, wd732
	set 0, [hl] ; count play time
	call ResetPlayerSpriteData
	ld c, 20
	call DelayFrames
	call Func_5cc1
	ld a, [wEnteringCableClub]
	and a
	ret nz
	jp EnterMap

This seems to suggest that this text, despite being translated into all languages and previously thought to be used in the case of a "memory error", was instead meant to be debugging text that was meant to ensure the memory for Yellow Version features was enough.

Weirdly, the Japanese version of the text calls the game Yellow Version (イエローバージョン) , instead of Pokémon Pikachu (ポケモンピカチュウ). This, combined with an earlier title screen, and mentions of "Yellow" in the game's source code, suggests that the game was intended to be called "Pokémon Yellow" in Japan as well.

(Source: pret Pokémon Yellow disassembly, SatoMew)

Version Differences

Revisional Differences

To do:
Document the other changes in Japanese Yellow revisions 1, 2 and 3.

Introduction Cutscene

The two screens which precede the opening cutscene were changed during the game's localization. In the first, the copyright dates were updated. As for the "Game Freak presents" screen, the "presents" graphic doesn't appear for some odd reason, despite it still being found in the VRAM.

Japan International
PKMN Y J Copyright Screen.png PKMN Y U Copyright Screen.png
PKMN Y J Game Freak Presents.png PKMN Y U Game Freak Presents.png

Title Screen Changes

The title screen had the logo changed to its international equivalent, the "POCKET MONSTERS" subtitle was removed, the copyright dates were updated, the "Yellow Version" subtitle was added, and the speech bubble was not only repositioned, but its contents were also changed from a stylized "ピカチュウ" (Pikachu) to a simple "Pika!". Border-wise, "POKEMON PIKACHU" was unsurprisingly changed to "POKéMON YELLOW".

Japan International
Japanese Pokémon Yellow Title and Border.png International Pokémon Yellow Title and Border.png

The "Pocket Monsters" to "Pokémon" change also affects the printable score screen for the Pikachu's Beach minigame:

Japan International
Pokémon Yellow Pikachus Beach Print Score JP.png Pokémon Yellow Pikachus Beach Print Score EN.png

Game Boy Color

(Very minor) Game Boy Color enhancements were added to the international releases. The game's marketing oddly tended to overlook this, implying this was a late change; unlike most titles, the front of the box provides no indication of this upgrade, and in some countries, the screenshot of GBC mode on the back of the game's box was omitted.


A lot of the changes which took place in Red and Blue still apply here. For example, while the overworld tileset was updated for this version, all the tile changes which existed in Red and Blue still apply to their respective localizations. Meanwhile, the town map screen features the same differences between the Japanese and International versions.

Revision 1

Technical Changes

The v1.1 release of Japanese Yellow ("Rev 1") changes the contents of restart vector 0x38 (rst $38) from jp F080 (arbitrary code execution in Echo RAM of D080 on an actual Game Boy) to point to another rst $38 (0xFF). The purpose of this original jp F080 is unknown, except it appears too in some other Game Boy games such as Bonk's Adventure and may have been some kind of debug handler.

The later change to another rst $38 is the cause of the infamous blue bar freeze pattern which was carried forward to the localisations as well, because the continuous jump back to 0x38 overwrites the stack and later the rest of the memory, including the VRAM with a continuous 00 39 pattern.

Revision 1 also alters some unidentified data. A byte comparison reveals many changes, but it is unknown which (if any) have a notable effect on the gameplay, and lots are simply a result of data being moved around. Other than updates to pointers, some data/code starting from 0x68 has been altered for unknown reasons.

Another example of a change is the data block at 0xF32AA (in bank 0x3C after Vermilion Gym trash can data), which has been greatly altered.

(Source: CasualPokéPlayer/Torchickens)

Revision 2

Technical Changes

The v1.2 release of Japanese Yellow ("Rev 2") makes some further changes of unknown significance. The earliest change is at offset 0x69 (byte 0x30 is now 0x20) and to some of the bytes which follow it. Additionally, there are some additional changes to the previously mentioned data block at 0xF32AA, but these are more minor compared to the differences between the initial release and rev 1 and consist of some occasional single byte changes.

Revision 3

Bug Fixes

The v1.3 release of Japanese Yellow, also known as "Rev 3", fixes a bug in which having Pikachu stand on one of the boulder switches in Victory Road will remove its corresponding wall tiles (as if the player pushed a boulder on to the switch) for all boulder switches but the one found in 1F. This fix was carried over to all localized versions of the game.

(Source: Legendary Starblob, ChickasaurusGL (Rev 3 detail))
Technical Changes

The earliest change is again to data around 0x68. A huge amount of data has also been wiped out with 00 bytes (such as the data block at 0xF32AA).

For text files of every single byte change, see this page.

To do:
The link is dead following the discontinuation of the old Google Sites. Reupload the file comparisons elsewhere.

Virtual Console Release

Jynx's sprites in the International Virtual Console re-release were updated to match the Pokémon's updated skin color. This effect was achieved by some of the 8×8 tiles composing the sprite being assigned an altered palette where black is replaced with purple. This technique was not used for any other Gen I or II sprites, making Jynx the only Pokémon in any of these games to have a sprite with more than four colors.

International GBC International VC
PokemonYellowJynxorig.png PokemonYellowJynxBattleorig.png PokemonYellowJynxvc.png PokemonYellowJynxBattlevc.png

Move Animations

The following move animations were changed slightly to avoid rapid flashing; as usual, this is to comply with current seizure protection standards.

  • Blizzard
  • BubbleBeam
  • Confusion
  • Dream Eater
  • Explosion
  • Guillotine
  • Hyper Beam
  • Mega Kick
  • Mega Punch
  • Psychic
  • Reflect
  • Rock Slide
  • Selfdestruct
  • Spore
  • Thunderbolt
(Source: Serebii)

Game Boy Printer

The option to print Pokédex entries using the Game Boy Printer was disabled on the Virtual Console. Other Game Boy Printer features were left unmodified, though this means little since the Game Boy Printer cannot be connected to the Nintendo 3DS.


Wireless trading was included in the Virtual Console release via the use of a modified emulator that spoofed the Link Cable without affecting the ROM. Moreover, the line "The link has been closed because of inactivity. Please contact your friend and come again!" was changed to "Please come again!"

Pikachu's Beach

The Pikachu's Beach minigame was made available to the player's starter Pikachu regardless of whether it knows Surf. However, the three posters in the Summer Beach House are still programmed to only give the player surfing tips if their party contains a Surfing Pikachu.

Unused HOME Menu Banners


Every language release in every region includes a placeholder HOME Menu banner in banner.cgfx. Two strange things stick out about this placeholder: First, the text indicates it's the HOME Menu banner for a Virtual Console release of Ninja Gaiden Shadow (Japanese: Ninja Ryūkenden GB ~Matenrō Kessen~)...except that game was never released for Virtual Console. Second, the release year given is 1989; Ninja Gaiden Shadow was released in 1991.

The Virtual Console releases of the core series Pokémon games are also unique in that almost every release contains HOME Menu banners for every possible language-region combination, for a total of 17 banners including the aforementioned placeholder (the only exception being the Korean Pokémon Silver, which is missing North American French, Spanish, and Portuguese). Of these, only the banner matching both the region and the language of the user's 3DS console is used. Part of the reason for this may be that the English, Spanish, and French releases are identical between North America and Europe. However, equivalent banners exist for South Korea, where Yellow was never released, not even for Virtual Console. This is simply a copy of the North American English banner in every release.