Pokémon Yellow

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.

Sub-Pages#

Development Info Prototype Info Notes Bugs

Leftovers#

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)

Translation Errors
Yellow changed the dialogue of one of the NPCs in the Celadon Department Store to say that he plans on gifting a Poké Doll to Copycat. However, the English version mistakenly states that Copycat lives in Cerulean City, as opposed to Saffron City. This mistake was caught in all other localizations, besides the Spanish one.

The Italian version of Yellow also came with a pretty egregious mistake, accidentally overwriting the message shown when using Teleport in the overworld with a copy of the message used when using Strength.

Main article: Pokémon Red and Blue

Unused Trainers#

Generic Trainers#

These rosters and the trainers associated with them are never used at any point in the game. Most of this data is identical to Red and Blue, including Prof.Oak's unused rosters.

Rocket Trio#

Four Yellow-exclusive unused entries, found right after the newly added roster data for the Rocket Trio. In Yellow, Jessie and James are an extension of the main "Rocket" class, with special code to change the trainer pic based on the roster ID. However, there is a redundant check for IDs 2E and beyond to also change the trainer sprite to the Rocket Trio one. Development data shows that Jessie and James started off with individual trainer sprites, and so it comes to reason that they were originally fought individually, with Jessie having rosters 2A through 2D, and James 2E through 31. While Jessie's data was overwritten, James' remains untouched, and consists only of his trademark Koffing/Weezing (meaning Jessie likely only had Ekans/Arbok). The devs ultimately combined the two into a single "new class", also adding Meowth as a part of their team.

Unused Audio#

Unused Cries#

(Headphone warning: these audio clips are loud and harsh!)

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

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.

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.

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!"/「はやく　にげるのじゃ！」. 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.

Unused Radness Bonus#

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.

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.

Unused Catch Rates#

Pokémon Yellow has a special feature regarding Generation II's Time Capsule, which will translate a Pokémon's catch rate into a held item when transferred. Dragonair and Dragonite's catch rates were lowered from 45 to 27, for Dragonair, and 9, for Dragonite. This makes them harder to catch, though neither Pokémon are wild encounters in Red and Blue. This also changes their held items from a Bitter Berry, in Red and Blue, to a Protein when Dragonair's transferred from Yellow , and Antidote for Dragonite.

While Dragonair can be found in the wild in the Safari Zone in Yellow, there is no way to encounter a Dragonite.

Unused Graphics#

Leftovers#

The unused overworld sprites, unused tiles, and unseen areas all make a return from Red and Blue, unsurprisingly completely untouched. One of the few exceptions is Koga's original overworld spriteset, as Koga in Yellow uses the male Silph worker spriteset instead.

The other outlier is Clefairy's walking sprites. Only the left/right ones are used in Yellow, due to Clefairy using new overworld sprites instead of the generic Clefairy ones.

Game Freak Tiles#

While these tiles are used in the Japanese version, during the "Game Freak" intro slide, they are never used in releases outside of Japan. The exact same thing also happened back in Red and Blue.

Title Screen#

The localized title screen feature four unused tiles. The first is the backdrop behind the N, which matches with the Red and Blue logo. It is even loaded in VRAM, leaving its absence strange. The second tile is intended to fit below the "P", but is never needed, as it is cut off by the "Yellow" subtitle. The last two tiles are meant for the bottom half of the "N", that is also cut off by the "Version" subtitle. As they are leftovers untouched from the Red and Blue logo, they are misaligned, placed two pixels too low.

Original	Mockup

Early Japanese Title Screen#

An early version of the Japanese title screen graphics, which still remains in the international releases 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 part of the title graphic, instead of being a separate, overlaid, sprite, and its placement suggests that it isn't a speech bubble.

Notably, there is a "Yellow Version" subtitle, making 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."

This early logo's tile arrangement looks closer to the one from Red and Green, and Blue's, with the "POCKET MONSTERS" subtitle under the "ポケットモンスター" logo.

Blue Title Screen	Yellow Title Screen (Mockup)	Yellow Title Screen (Final)

Middle-Aged Woman#

Unused Frames	Animated Sprites

The middle-aged woman NPC was given a proper side walking sprite in Yellow, though it still remains unseen. These sprites were later used in Pokémon Gold and Silver, as this spriteset was assigned to the newly introduced Pokéfan class.

Officer Jenny#

Unused Frames	Animated Sprites

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

Bulbasaur#

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

Pikachu's Beach#

There are a few unused sprites intended for the "Pikachu's Beach" minigame:

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 they aren't on the surfboard.

Two unused sprites saying "GOOD!" and "YEAH-", which may have been intended as compliments for either good gameplay or successful flips.

Japan	International

An unused message in the same style as the "START" and "OH NO.." messages that display when starting and ending the minigame. This one was likely meant for finishing the course. This sprite only exists in the Japanese and English versions, and was blanked in other localizations.

Tileset 00#

The unused flower tile from the previous games returns here, but this time it is also found in tileset 00, instead of just in tileset 07. Just as before, however, it still is overwritten in-game, meaning you never get to see it in action.

Original	Mockup

Tileset 13#

The tileset for the Summer Beach House on Route 19, has two unused tiles. They both form halves of a 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

Surfing Tileset 2#

The tileset for the Surfing Pikachu mini-game on Route 19, has seven unused tiles. They are Japanese characters leftover from the initial overseas release of Pokémon Yellow.

Tileset	Unused Tiles

Unused Blocks#

Tileset 00#

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

Tileset 19#

• 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, and found right after the standard "Got away safely!" string. It's spoken as an old man would speak in the Japanese version, hinting that this line was intended for Professor Oak.

Sea Cottage
Likely would've been uttered by Bill if you tried to leave his house without helping him first, 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 final game, you can leave the house at any point without anything dissuading you, much like in Red and Blue.

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.

System Text#

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

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

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.

Not Enough Memory#

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

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

Func_5cc1:
; unused?
    ld a, $6d
    cp $80
    ret c ; will always be executed
    ld hl, NotEnoughMemoryText
    call PrintText
    ret

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:

check_p_area:
    ld    a,p_bottom - p_top
    cp    128
    ret    c

    ld    hl,over_msg$
    call    put_win_msg

    ret

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
SpecialEnterMap::
    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.

Version Differences#

Revisional Differences#

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

Introduction Cutscene#

The two screens preceding the opening cutscene were updated during localization. The copyright dates were updated, and on the "Game Freak PRESENTS" screen, the "PRESENTS" graphic was removed, despite it loading into VRAM.

Japan	International

Title Screen Changes#

The "POCKET MONSTERS" subtitle was removed, the copyright dates were updated, the "Yellow Version" subtitle was added. The speech bubble was shrunk down and moved, but the text was changed from "ピカチュウ" (Pikachu) to a simple "Pika!". "POKEMON PIKACHU" was changed to "POKéMON YELLOW" for the Super Game Boy border.

Japan	International

Pikachu's Beach Changes#

The Pikachu's Beach mini-game's title "ピカチュウの サマービーチ" (meaning "Pikachu's Summer Beach") was localized simply as "Pikachu's Beach":

Japan	International

The Beach mini-game's "Start" and "Oh no.." graphics have been localized:

Japan	International

The Beach mini-game's score screen updated "Pocket Monsters" to "Pokemon":

Japan	International

Game Boy Color#

The game added additional colors for the Game Boy Color in all localized releases. Not all relevant countries printed this feature blurb, or the example screenshot, on their boxes, hinting at it being a late addition.

Red and Blue Holdovers#

Being built off Red and Blue, Yellow retains all of the updates made for those games, too. While the overworld tileset was updated for Yellow, International Red and Blue's International tile changes still apply.

Also, the same town map differences exist 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. This also appears in 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 over to localizations as well. The continuous jump back to 0x38 overwrites the stack, and then all usable memory, with a continuous 00 39 pattern.

Revision 1 made changes, though it's unknown how this affects gameplay. Some data starting around 0x68 has been altered, though.

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

Revision 2#

Technical Changes

A few bytes were changed in many places, namely at offset 0x69, as byte 0x30 is now 0x20, and some following data. There's also minor changes to the data block at 0xF32AA.

Revision 3#

Bug Fixes

The Japanese Version 1.3 release fixes a minor bug. Having Pikachu stand on one of the boulder switches in Victory Road, instead of pushing a boulder onto it, will remove all barrier walls, except for the one on the first floor of the dungeon. This fix was included on all localized versions.

Technical Changes

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

Download Japanese Yellow File Comparisons File: Japanese Yellow file comparisons.zip (3,51 MB) (info)

Virtual Console Release#

Jynx's sprites in International Virtual Console releases were updated with the new, purple skin color. This makes Jynx the only Pokémon to have more than four colors, in Gen I or II, due to how this was done: by replacing some 8x8 tiles' black color with a purple one instead.

Move Animations#

As a precaution to avoid seizures, the following move animations were changed to avoid rapid flashing.

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

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.

Trading#

Wireless trading was included in the Virtual Console release, by emulating 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.

However, there are two strange things about this banner: First, the text indicates it's the HOME Menu banner for a Virtual Console release of Ninja Gaiden Shadow, but that game was never released for Virtual Console.

Second, the release year given is 1989; Ninja Gaiden Shadow was released in 1991.

Also, the game chooses a banner based on what combination of region and language your 3DS is. For some reason, there is an equivalent banner for South Korea, but Yellow was never released there, not even for Virtual Console. This banner re-uses the North American English banner, though.

References#