Pokémon FireRed and LeafGreen

Pokémon FireRed and LeafGreen are remakes of the first two Pokémon games, Red and Green. Aside from a graphical overhaul, features from Ruby and Sapphire were carried over, alongside many new elements, most notably the Sevii Islands. The games were re-released on February 27, 2026 for the Nintendo Switch as an eShop download, recompiled to enable exciting new features like not being able to swear at your Pikachu anymore.

Development Info Prototype Info Prerelease Info Bugs Untranslated Text DumpText found within the game that wasn't translated, including some leftovers from Ruby and Sapphire. Regional DifferencesA few more changes this time around. Unused GraphicsPoor Tuber didn't stand a chance… Unused MapsSevii Islands leftovers, and more!

Build Dates#

Located near the start of the main function in the ROM. The Nintendo Switch version adds an 8-character commit hash to the end of the build date, because there's this little thing called "Git" you may have heard of in the 22 years since FRLG came out.

Assert Paths#

Near the build date info is a plain-text string showing the build path and a few expressions from the source code; these are generated by an assert macro, to be printed to a debugger via AGBPrintf when an assert fails. The Japanese 1.0 revisions use relative paths instead of the full paths, both English revisions (1.0 and 1.1) have this line in full, and the Japanese 1.1 revisions and Nintendo Switch version no longer have this information.

• FireRed JP 1.0 (location 1CDE8A) and LeafGreen JP 1.0 (location 1CDE66):

../gflib/malloc.c
 0
 p != NULL
 pos->magic_number == MALLOC_SYSTEM_ID
 pos->flag == TRUE
 pos->next->magic_number == MALLOC_SYSTEM_ID
 pos->prev->magic_number == MALLOC_SYSTEM_ID

• FireRed US 1.0 (location 1E9F68), LeafGreen US 1.0 (location 1E9F44), FireRed US 1.1 (location 1E9FD8), and LeafGreen US 1.1 (location 1E9FB4):

C:/WORK/POKeFRLG/src/pm_lgfr_ose/source/gflib/malloc.c
 0
 p != NULL
 pos->magic_number == MALLOC_SYSTEM_ID
 pos->flag == TRUE
 pos->next->magic_number == MALLOC_SYSTEM_ID
 pos->prev->magic_number == MALLOC_SYSTEM_ID

Debugging Functionality#

To do: Search for more.

Sound Check#

At least Japanese FireRed v1.0 has the Sound Check like Ruby and Sapphire, except it was removed in localizations this time around.

To access it, patch 0x12f342 to 00 00 00 00 and 0x12f35c to 01 FF 09 08 in a Japanese FireRed v1.0 ROM to replace the New Game entry on the main menu with a call to Sound Check (this has the effect of running Sound Check after the title screen if there is no save file).

The misspelling of the word "stereo" in the Driver Test from Ruby and Sapphire was fixed in the equivalent of FireRed and LeafGreen as well as of Emerald, being now correctly spelled in katakana (ステレオ) instead of hiragana (すてれお), and the entry itself was also moved to the bottom.

Ruby and Sapphire Leftovers#

Dusclops Palette Oddity#

Dusclops has a single yellow color in its palette that isn't used anywhere, right beside its eye's palette, and it's both on the normal and the shiny palette, suggesting this color was used late into development before being scrapped. This oddity also exists in Ruby and Sapphire, as non-gen 1 Pokémon (except Teddiursa, for whatever reason) did not receive new sprites for FireRed and LeafGreen.

Unused Timer Ball Frame#

This Timer Ball frame from Ruby and Sapphire remains unused for the same reason.

Unused	Used

Key Items#

Since key items cannot be transferred with a Pokémon, they're unused and most have no effect in FireRed/LeafGreen. The Mach Bike and Acro Bike do work, but act like the normal Bicycle, though they can't be used on the Cycling Road. HM08 (Dive) also works and can be taught to Pokémon, but unlike normal HMs, the move can be deleted freely. Despite this, Pokémon knowing Dive cannot be transferred to Generation IV games until the move is forgotten.

Base Decorations#

Every secret base decoration and its associated data remains unused within FireRed and LeafGreen; descriptions for these items also remain.

Trainer Sprites#

A lot: Archie and Team Aqua, Maxie and Team Magma, Beauties, Cyclists, Hex Maniacs, Gym Leaders, the Elite Four and Champion, etc. While you can battle them in-game through hacking, their Pokémon data is gone, so they don't have any Pokémon to battle with except for Level 5 Ekans. (Or, in the case of the Tubers, Level 38 Starmie, which, itself, is a copy of Swimmer Male Finn's first party on Kindle Road.)

Tilesets#

The indoor tileset and palette from Ruby and Sapphire is leftover at 0x2D4CD4. The block data is also intact, but in a broken state.

Weather#

Most overworld weather goes unused, except for regular fog.

Since rain no longer occurs naturally, the related battle message is now unused.

あめが　ふっている

It is raining.

In both FireRed and LeafGreen, attempting to load overworld sun in any location freezes the game; music continues playing, but the player is stuck on a black screen and can't continue.

Scripts#

Multiple scripts starting at 0x1638EC in the US 1.0 version remain as leftovers from the first Braille chamber, with the alphabet inscribed in groups of three (ABC, DEF, GHI ...). A room similar to it was likely planned but then scrapped in favor of having a Braille table included in the booklet.

Dive Script#

Starting at 0x1BE38B in the US 1.0 Version is the script for checking and prompting the player to use Dive leftover from Pokémon Ruby and Sapphire, along with the behavior byte used for dive tiles.

Additionally, Dive, despite not being used or being available as a HM in this game, still prevents transfer of Pokémon with the move to Diamond, Pearl and Platinum.

Music and Sound Effects#

To do: Confirm that the PokéNav and Contest effects are in fact unused and not repurposed.

SE-TRACK-MOVE (sound effect 2B)

SE-TRACK-STOP (sound effect 2C)

SE-TRACK-HAIKI (sound effect 2D)

SE-TRACK-DOOR (sound effect 2E)

Above tracks were used for the moving truck from Ruby, Sapphire and Emerald. Since FireRed and LeafGreen don't have moving trucks, these go unused.

MUS-ME-KINOMI (music 106), used for Berry picking from trees.

Overworld Sprites#

Name	Sprites	FireRed Offset	LeafGreen Offset
Brawly		369F28 - 36A227	369F08 - 36A207
Rich Boy/Contestant		372AA8 - 3733A7	372A88 - 373387
Camerman		38D5A8 - 38DEA7	38D588 - 38DE87
Running Triathlete (Female)		384828 - 385127	384808 - 385107

The graphics for Brawly, the Cameraman and the Rich Boy/Contestant have no palette nor frame data assigned to them, but the Running Triathlete does. This has been copied directly from Ruby and Sapphire, however using this in FireRed and LeafGreen results in the sprite being coloured differently as the palette tag ID (1104) now describes a different palette:

Ruby & Sapphire Palette	FireRed & LeafGreen Palette (Unused)

Unused Battle Environment#

To do: I think underwater should still be covered, just with a side-by-side comparison.

Long grass and underwater do not exist in FireRed and LeafGreen, but their environments (0x1 and 0x3, respectively) are still present. Notably, while underwater is pretty much identical to Ruby and Sapphire version, with only a slight shift in palette, long grass is quite different, using FireRed and LeafGreen's tall grass platform with a completely unique palette for the background.

Unseen Text#

• While not technically unused, this text requires cheating to be seen. If the player interacts with the TV on the ground floor of their house from the sides or back, almost the same text string as from Pokémon Red and Blue appears. The only difference is that FRLG has two extra dots at the end (in the English script)/removed a "ぞ" from the end of the sentence (in the Japanese script).

Oops, wrong side...

みえない・・・・ 

• Pokémon 0000 (Ten question marks) is an error handler which doesn't appear under normal gameplay. Unlike in Ruby, Sapphire and Emerald, if this caught by manipulating the game, it might show a glitched Pokédex entry or one for another valid Pokémon. Nevertheless, it has a fully-coded Pokédex entry in the data. Note some wording differences across languages (vs. Ruby, Sapphire and Emerald).

• The map headers for the unused Sevii routes were localized, with the Spanish version getting a little creative, using made-up names instead of plain numbers, like in the used maps.

• Wally's text from Ruby and Sapphire's catching tutorial persist into the files of this game. The text's address is at 3FDAB1.

You throw a BALL now, right?
I... I'll do my best!

• The "move combining" text for Heat Wave persisted too, just as unused as it was in Ruby and Sapphire. The text's address is at 3FCFC2.

The wind turned into a
HEAT WAVE!

Unused Music#

A chiptune-like version of the MUS-ME-ASA (music 0100), the "Pokémon Healed" theme, which sounds like the original from Red and Blue. It has the label MUS-KAIHUKU in Sound Check and its ID is 0119.

Shiny Celebi#

For the sake of consistency, every Pokémon in every game is given a Shiny variant, and Celebi is no exception. However, because the only way to obtain it legitimately was through distributions, the Shiny version of Celebi was left unobtainable through normal means. This sprite may still be seen (in a lighter hue) if a Shiny Pokémon transforms into a Celebi. Like "standard" Celebi and many other Pokémon, the sprite is identical to that of Ruby and Sapphire, where it was similarly unobtainable. While Shiny Celebi was previously available in Pokémon Crystal, it was solely locked to the Japanese version and couldn't be brought up to future games. This changed with the 3DS Virtual Console release, which allowed Celebi to not only be caught in any language version of Pokémon Crystal, but could also be sent into future games via Pokémon Bank.

Altering Cave#

Mareep, Aipom, Pineco, Shuckle, Teddiursa, Houndour, Stantler, and Smeargle were meant to replace the Zubat found in Altering Cave after using Mystery Gift. The event distribution was probably scrapped because these Pokémon can be obtained from Pokémon Colosseum or Pokémon XD: Gale of Darkness, as well as in Emerald on the extended area of the Safari Zone (except Smeargle, which is found in Artisan Cave instead) - despite the fact Emerald also has an Altering Cave with the same design and (lack of) implementation.

Technically, this is implemented by its map script reading a numerical variable and selecting from one of 10 encounter tables (all of which specify only 1 Pokémon).

The game does contain a built-in implementation of an Altering Cave event, which attaches to the deliveryman in the top floor of the Pokémon Center and sequentially switches the selected Pokémon then displays:

Thank you for using the MYSTERY
GIFT System.

Recently, there have been rumors
of rare POKéMON appearances.

The rumors are about ALTERING
CAVE on OUTCAST ISLAND.

Why not visit there and check if
the rumors are indeed true?

ふしぎなおくりもの を ごりよう
いただき ありがとう ございます!
さいきん はずれのしま にある
へんげのどうくつ で
めずらしい ポケモンが でる という
うわさが ながれてる ようです\cぜひ いって たしかめて みては
いかがで しょうか? 

This, however, may not necessarily be indicative of how an official event would have worked.

Unused Code#

To do: Isn't this in Ruby and Sapphire?

Diagonal Movement#

The movement table, located at 3A64C8, contains the directions the player or an NPC must move in. However, after the first five entries (steady, down, up, left, right), four more follow, resulting in diagonal movement when activated. Using them results in some glitches with warps and map rendering. It should be noted that the games feature buildings with otherwise strange diagonal corners, contrasting with the buildings of the original games.

A video showcasing this diagonal movement can be seen here.

It should also be noted that there are two instances where this type of movement IS used. The first is during the end credits, when the camera pans over the map. The second is in Pokémon Emerald when the camera pans over to Groudon and Kyogre once you fly back to Sootopolis after awakening Rayquaza.

Diagonal movement wasn't implemented for characters or NPCs in any final version until the release of Pokémon X and Y three generations later.

Wild Double Battles#

Some data suggests wild double battles were originally planned for this generation, but were delayed until Generation IV. For example, a string "Wild [buffer1] and [buffer2] appeared!" is located at 3FD2BF, and setting only bit 0 in the battle type flag at 02022B4C in the RAM results in such a battle, if used at the right moment.

As with the previous feature, it isn't finished and may result in some bugs.

Unused Trainer Battles#

There are several unused trainer battles in the game. Most of them are dummy battles where the battler only has one level 5 Ekans. However, a few have real teams and some of them are cut trainers that existed in Red and Blue. There is one trainer battle in the game for every cut Ruby and Sapphire trainer battle sprite. To experience the battles in-game, the following address has to be frozen to the desired Trainer Battle ID and then any trainer battle has to be initiated.

Unused Trainer Classes#

To do: Put the Player and PKMN Prof. classes in a table and add their IDs.

There are two new unused trainer classes that were added in FireRed and LeafGreen, but are used by unused trainers. These are the Player and PKMN Prof. classes. The former is used four times, and uses the trainer sprites for Red, Leaf, Brendan and May. The latter is used only one time, where it is used for Professor Oak himself as well as his sprite, possibly implying that the unused battle with Oak from the originals was going to be used in this game.

Unused Held Items#

Some Pokémon, when found in the wild, have a chance of holding an item. This held item data also exists for some Pokémon which cannot be caught in the wild in the final games. Given how the held item data was carried over, some of these sets are actually used in later series entries.

Unless specified otherwise, all members of a given line share the same held item roster.

Revisional Differences#

North America received a v1.1 revision of FireRed and LeafGreen which fixed a couple things. Those changes were taken into account for the non-English European localizations.

US v1.0	US v1.1

• Version 1.0 of the North American release does not show "PRESENTS" on the Game Freak logo screen, although its graphics remain intact. Both Red and Blue and Yellow also lacked the presents text in their localizations, so it may have been an intentional nod. It was later changed in v1.1, now matching the Japanese versions, as well as the international releases of Ruby, Sapphire, and Emerald.

• Version 1.1 fixed a coding mistake which caused category names in the Pokédex to only display the first word, due to the game incorrectly interpreting the space character as a terminating byte. For example, this issue would cause Pidgey to be listed as the "Tiny Pokémon" rather than "Tiny Bird Pokémon".

• Version 1.1 fixed the description of the Help Menu's "Reading the Pokédex" tab. It originally referred to the "NEXT DATA" option by its Generation I equivalent, "AREA". This error was already present in the Japanese versions of FireRed and LeafGreen, with the help tab using "ぶんぷ" instead of "つぎのデータ".

• Version 1.1 fixed Chikorita's FireRed Pokédex entry, now correctly referring to a singular "leaf".

• In v1.0, Tyranitar has the same Pokédex entry in both FireRed and LeafGreen, with it being reused from Gold. In v1.1, Tyranitar has a new Pokédex entry in FireRed, which is a retranslated version of its Silver entry.

Nintendo Switch Changes#

To do: There's many changes in the Switch revision a couple of which still need documentation/confirmation such as photosensitivity changes and Mystery Gift.

The Nintendo Switch re-releases of Pokémon FireRed and LeafGreen use a newly compiled ROM that contains several changes from the Game Boy Advance releases, in addition to the changes made in version 1.1. Many of these changes call interrupts implemented by the emulator that do not exist on a real GBA, making the new ROM unplayable on real hardware. The changes are primarily modifications to the link cable code to enable the new online functionality, but there are also some changes to gameplay, listed below.

Profanity Filter#

Watch on YouTube

Whenever the player is given the option to input text (such as when naming the player character/rival, nicknaming a Pokémon, or renaming a box) it is checked for profanity. If profane language is detected, the game will treat the input as if it was blank. This is likely to prevent players from trading Pokémon with inappropriate nicknames or OTs to other players or from transferring them to Pokémon HOME. The original games lacked any kind of anti-profanity feature, as text filtering wasn't introduced until Generation V (for newly nicknamed Pokémon) and Poké Transporter (for Pokémon transferred from previous games).

To implement the profanity check, the developers added code to the ROM to call interrupt 0x4d whenever text has been entered; the emulator catches this interrupt, passes the text through the Switch's internal profanity filter and returns the filtered text to the game.

ROM Differences#

To do: Document other notable changes to the ROM as they are discovered.

The original Game Boy Advance releases of Pokémon FireRed and LeafGreen had two revisions released, revisions 0 and 1. The ROM used by the Nintendo Switch version appears to be a new "revision 10"¹¹ which was compiled on December 19, 2025 at 4:01pm.

Roar Glitch#

In the original releases, if a roaming Pokemon used the move Roar to end the battle (applicable only to Raikou and Entei), then it will never be encountered again because the game incorrectly flags it as defeated. In the Nintendo Switch version, this bug has been patched and as a result, Raikou and Entei can still be encountered again if they use Roar successfully.

Berry Program Update#

The original releases of Pokémon FireRed and LeafGreen contained a program available by pressing Select and B on the title screen called the "Berry Program Update" which could be used to patch the berry glitch present in Pokémon Ruby and Sapphire. Although the Berry Program Update is still included in the ROM, the button combination needed to activate it has been commented out, rendering it unused.

AuroraTicket and MysticTicket#

The code in the ROM has been updated to automatically place the AuroraTicket and the MysticTicket in the player's bag upon entering the Hall of Fame if at last, one of the Pokemon in the party don't have the Champions Ribbon, along with setting the flags necessary to activate their respective events. Originally, these items could only be obtained from real-world distribution events, but they have been made accessible to all players in the re-release, following the lead of Pokémon Crystal's 3DS Virtual Console release. Presenting these tickets to the sailor in Vermilion City (after first receiving the Rainbow Pass from Celio) allows the player to access Birth Island and Navel Rock, respectively, to battle Deoxys, Ho-Oh and Lugia.

Controls#

With the button mode in the game’s options set to either HELP or L/R, all the GBA buttons are mapped as you'd expect, with X and Y being mapped to Start and Select respectively. With the button mode set to L=A however, quite a number of functions on the regular control scheme are now shuffled around: Movement is now mapped to both analogue sticks, while the D-Pad (or D-buttons) double as a second set of face buttons. R now also duplicates the A button and both ZL and ZR now double as B. This allows for a one-handed control style similar to using a single Joy-Con in the Let's Go games. This same functionality can be accessed by playing with only one Joy-Con in any of the other button modes. The SL and SR buttons will also function as L and R buttons this way.

References#