Development:Pokémon Yellow

This page details development materials of Pokémon Yellow.

This page or section details content from the April 2020 Nintendo Leak. Check the April 2020 Nintendo Leak category for more pages also sourced from this material.

This page or section details content from the October 2024 Game Freak Leak. Check the October 2024 Game Freak Leak category for more pages also sourced from this material.

Pokémon Pink

The leaked source code for Yellow includes a few mentions of a seemingly never made companion version that would've been called Pokémon Pink. This includes "Pocket Monsters Pink & Yellow", as well as pokemon_type in PM_DEBUG.DEF having the options "yellow package" and "pink package" (although the "pink package" only has a minor effect on the game tied the original Red/Green such as the gender of a Nidoran NPC.).

While it is not certain which Pokémon would have been the mascot of Pink, Clefairy appears to be the most likely candidate, given its coloration and the fact it was originally intended to be the franchise's mascot. An image of a frame that was included in the Japanese release of the Game Boy Camera appears to corroborate this.

Early Sprites

GS Source Files

These sprites were found at the very end of a list containing several sprites for an early version of Pokémon Gold and Silver, which itself was found within leaked material for that game. This isn't surprising, as Yellow was being developed around the same time as Gold and Silver. These sprites are labeled with the filename format "PMYF_" ("Pocket Monsters Yellow Front") followed by the corresponding Pokémon's Pokédex number. Worth noting is that Squirtle and Kakuna are also found within this listing, but weren't included in this table due to them already being finalized.

Pokémon Name	Early Sprite	Final Sprite	Notes
Charmander			Similar sprite, albeit with a different facial expression, and some missing detailing. This early sprite is directly based on this artwork of Charmander from the original series anime, whereas the final sprite made it more unique.
Caterpie			Totally different sprite, which is based on this artwork of Caterpie, whereas the final sprite instead used this one as a base.
Butterfree			Similar sprite, albeit with less dynamically posed feet, a narrower body and face, and a slightly less refined left eye and mouth. This early sprite is directly based on this artwork of Butterfree, whereas the final sprite made it more unique.
Weedle			Similar sprite, albeit quite rougher and larger than the final one. Both based on the same piece of artwork.
Rattata			Totally different sprite, which is based on this artwork of Rattata, whereas the final sprite went with a unique pose.
Raticate			Totally different sprite, which is rather rough, and appears to be based on Ratticate's Red and Green artwork. The final sprite instead uses this artwork as a base.
Spearow			Totally different sprite, which is based on this artwork of Spearow, whereas the final sprite went with a unique pose.
Arcanine			Similar sprite, albeit flipped horizontally and less refined. Both based on the same artwork.
Farfetch'd			Similar sprite, albeit with less dynamically posed feet, and with Farfetch'd holding the leek in one of its wings, instead of with its beak. This early sprite is directly based on this artwork of Farfetch'd, whereas the final sprite made it more unique.
Dodrio			Sprite is almost identical to the final, aside from some of missing shading and detailing. Both are based on the same artwork.
Jolteon			Totally different sprite, which appears to be based on Jolteon's Red and Blue artwork, albeit with a different facial expression. The final sprite instead uses this artwork as a base but with a face reminiscent of the early sprite.

Scratchpad Files

A set of .CBB files from the 2024 Game Freak data breach, found in HaveSomeFun__RandomFromBoxEnt under the pokemon yellow directory, which is split into two folders:

• The first is called "送信済み" (sent) and ranges from 1998/04/07 to 1998/06/03 according to file modified dates. Worth noting is that Zubat, Golbat, Magneton and Zapdos are also found within this listing, but weren't included in the table below due to them already being finalized.
• The second is called "更新" (update) and ranges from 1998/04/28 to 1998/06/05 according to file modified dates. Unique to this later folder are already-finalized Geodude, Graveler and Electabuzz sprites. All other sprites were finalized, aside from a few outliers, noted further down.

Pokémon Name	Early Sprite (送信済み)	Final Sprite	Notes
Ivysaur			Similar sprite, albeit flipped horizontally and less refined.
Venusaur			Sprite is almost identical to the final, aside from some of the detailing on the main body.
Wartortle			Totally different sprite, which is rather rough, and appears to be based on Wartortle's Red and Blue artwork.
Blastoise			Totally different sprite, which is rather rough, and is reminiscent of Blastoise's Red and Blue artwork.
Nidorino			Similar sprite, only less refined.
Nidoking			Totally different sprite, with Nidoking seen from the back, not unlike its early Capumon sprite funnily enough.
Meowth			Similar sprite, only much rougher, with a smaller head and one paw raised, instead of having both arms crossed.
Persian			Sprite is almost identical to the final, aside from some of the detailing around the face area, and being flipped horizontally.
Poliwhirl			The main body is identical, but the legs were redrawn, and the right arm and eye were touched-up to balance the pose.
Poliwrath			Totally different sprite.
Kadabra			Sprite is almost identical to the final, aside from the head and some overall detailing, and being flipped horizontally.
Alakazam			Sprite is almost identical to the final, aside from some detailing around the shoulders and knees, and being flipped horizontally.
Golem			An unfinished Golem sprite. What's there is close to the final sprite, aside from the right arm being out-stretched instead of bent.
Magnemite			Sprite is almost identical to the final, aside from the position of the screws.
Shellder			Totally different sprite.
Gastly			Sprite is almost identical to the final, aside from a portion of the darker smoke shade.
Haunter			Similar sprite, albeit rougher, and flipped horizontally.
Gengar			Sprite is almost identical to the final, aside from some of the detailing.
Drowzee			Lacks shading, and has a slightly different pose.
Hypno			Sprite is almost identical to the final, aside from a missing ear and some detailing.
Kingler			Similar sprite, albeit rougher, and flipped horizontally.
Voltorb			Sprite is almost identical to the final, aside from some of the detailing.
Electrode			Sprite is almost identical to the final, aside from the angle of the face.
Exeggcute			Sprite is similar to final, only rougher, and with the central egg being smaller. The sprite is also flipped horizontally.
Hitmonlee			Similar sprite, albeit rougher, and flipped horizontally.
Hitmonchan			Similar sprite, albeit rougher, and flipped horizontally.
Rhydon			Similar sprite, albeit rougher, and with a slightly different pose.
Horsea			Sprite is almost identical to the final, aside from some of the detailing, and being flipped horizontally.
Starmie			Sprite is almost identical to the final, aside from some of the detailing.
Scyther			Totally different sprite, which is rather rough.
Magmar			Similar sprite, albeit rougher.
Gyarados			Totally different sprite, which is rather rough, and is reminiscent of Gyarados' Red and Blue artwork.
Ditto			Similar sprite, albeit quite larger than the final one. The early sprite is directly based on this Ditto artwork.

Every sprite in "update" is finalized, aside from Venusaur (unchanged from "sent"), and the following three Pokémon (which are close to final).

Pokémon Name	Later Sprite (更新)	Final Sprite	Notes
Exeggcute			The right eye's pupil was shifted by one pixel.
Rhydon			The base of the tail was very slightly tweaked.
Gyarados			One black pixel in the left eye was replaced with light grey.

Early	Final

For some reason Abra's sprite in "sent" (dated 1998/04/28) is finalized, but the version in "update" (dated 1998/05/30) has a noticeably rougher head and different torso detailing.

Yellow Source Files

These sprites, meanwhile, were found within the Yellow source code leak:

Early	Final

An early sprite of Pikachu, which is more directly based on this artwork from the original anime series. Labeled here as PMYF_DMY.DAT (the used sprite instead known as PMYF_025.DAT), likely standing for "Pokémon Yellow Front Dummy", this was likely just a scrapped early sprite the devs decided to keep for some reason.

Early	Final

Separate sprites for Jessie and James, found, respectively, under ROCKET1.DAT and ROCKET2.DAT. The final game instead combined them into a single sprite, known as ROCKETS.DAT. Instead of both being fought individually, it's more likely the artist just kept the individual sprites in case they wanted to change their arrangement. The sprites are nearly identical to the final, with only a straighter leaf on James' rose; Jessie's left eye has one less pixel, while the heel of her back leg is angled further out.

A cropped sprite of Magby's early design from Gold and Silver's Spaceworld '97 demo. Given how it is known as TEST.DAT, it was likely used as some sort of placeholder.

A sprite of Nidoran taken from the old official Game Freak website, down to using the same filename, 029NIDO.GIF. Likely used as reference for Nidoran♀'s updated sprite.

Sounds

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

Found in the SOUND folder of the leaked source code. As it turns out, 74 of the original 151 Pokémon had their Japanese anime cries or sound effects digitized, but none of them made it into the final game besides Pikachu's. This is likely due to the poor quality of the converted clips, the fact many of them are harsh on the ears, and the lack of space to fit them all in. Moreover, since many Pokémon have different names and/or cries between languages, this also means they'd need different voice clips for all the languages they wanted to release Yellow in.

Small wonder the idea was scrapped!

Pokédex 001-050

Dex #	Japanese Name	English Name	Voice Clip
001	Fushigidane	Bulbasaur
002	Fushigisou	Ivysaur
004	Hitokage	Charmander
007	Zenigame	Squirtle
010	Caterpie	Caterpie
011	Toranseru	Metapod
012	Butterfree	Butterfree
013	Biidoru	Weedle
014	Kokuun	Kakuna
015	Supiaa	Beedrill
016	Poppo	Pidgey
017	Pijon	Pidgeotto
019	Koratta	Rattata
020	Ratta	Raticate
021	Onisuzume	Spearow
023	Arbo	Ekans
024	Arbok	Arbok
026	Raichu	Raichu
027	Sando	Sandshrew
035	Pippi	Clefairy
036	Pikushii	Clefable
037	Rokon	Vulpix
041	Zubat	Zubat
042	Golbat	Golbat
043	Nazonokusa	Oddish
044	Kusaihana	Gloom
046	Paras	Paras
048	Konpan	Venonat
049	Morufon	Venomoth
050	Diguda	Diglett

Pokédex 051-100

Dex #	Japanese Name	English Name	Voice Clip
051	Dugtrio	Dugtrio
052	Nyaasu	Meowth
053	Persian	Persian
054	Kodakku	Psyduck
056	Mankey	Mankey
057	Okorizaru	Primeape
063	Keshi	Abra
064	Yungeraa	Kadabra
066	Wanrikii	Machop
069	Madatsubomi	Bellsprout
070	Utsudon	Weepinbell
072	Menokurage	Tentacool
073	Dokukurage	Tentacruel
074	Ishitsubute	Geodude
075	Goroon	Graveler
079	Yadon	Slowpoke
080	Yadoran	Slowbro
081	Koiru	Magnemite
082	Reakoiru	Magneton
085	Dodrio	Dodrio
086	Pauwau	Seel
088	Betobeta	Grimer
089	Betobeton	Muk
092	Goosu	Gastly
093	Goosuto	Haunter
094	Gengar	Gengar
095	Iwaaku	Onix
096	Suriipu	Drowzee
097	Suriipaa	Hypno
098	Kurabu	Krabby
100	Biriridama	Voltorb

Pokédex 101-151

Dex #	Japanese Name	English Name	Voice Clip
104	Karakara	Cubone
106	Sawamura	Hitmonlee
107	Ebiwaraa	Hitmonchan
109	Dogaasu	Koffing
110	Matadogasu	Weezing
113	Rakkii	Chansey
114	Monjara	Tangela
116	Tattsuu	Horsea
118	Tosakinto	Goldeen
120	Hitodeman	Staryu
121	Starmie	Starmie
129	Koiking	Magikarp

Title Screen Mockup

Hidden in /yellow/Document/pika.bmp is a mockup image of the English Pokémon Yellow title screen. Pikachu's sprite, while blocky, appears to have been scaled through an algorithm other than nearest neighbor, as color blending can be seen along its edges.