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Jet Force Gemini

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Title Screen

Jet Force Gemini

Also known as: Star Twins (JP)
Developer: Rare
Publishers: Rare (US/EU), Nintendo (JP)
Platform: Nintendo 64
Released in JP: December 1, 1999
Released in US: October 11, 1999
Released in EU: November 2, 1999

AreasIcon.png This game has unused areas.
CodeIcon.png This game has unused code.
DevTextIcon.png This game has hidden development-related text.
EnemyIcon.png This game has unused enemies.
GraphicsIcon.png This game has unused graphics.
ModelsIcon.png This game has unused models.
MovieIcon.png This game has unused cinematics.
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.
PiracyIcon.png This game has anti-piracy features.

ProtoIcon.png This game has a prototype article
PrereleaseIcon.png This game has a prerelease article
NotesIcon.png This game has a notes page

One of Rare's lesser known AAA titles for the Nintendo 64, Jet Force Gemini didn't sell particularly well, only about a million copies and has never had a sequel. It was generally met with very solid reviews, despite being criticized for the somewhat clunky camera and stiff controls. It's also pretty gory for a T-rated game.


Read about prototype versions of this game that have been released or dumped.
Prototype Info
Read about prerelease information and/or media for this game.
Prerelease Info
Miscellaneous tidbits that are interesting enough to point out here.
JFG UnusedMap13.png
Unused Levels
There’s quite a few of these.
JFG 3DRarelogo.png
Unused Models
Unused Text

Debug Options

Debug Mode

A debug mode can be enabled by pressing C-Left, C-Right, C-Up, C-Down, R, L, L, R, C-Up, R, C-Down, R, L, C-Right at the title screen. A small box will appear at the bottom right corner of the screen, which displays various information such as the coordinates for player 1, current location, and the amount of free RAM.

The debug menu

Alternately, you can apply the following GameShark code for the same effect:

Version GameShark Code
USA 810A32D0 0001
Europe 800A3540 0001
Japan 800A3194 0001

Debug Cheats

A total of four debug cheats that were a part of the debug menu in the kiosk version of the game also remain in the final version. The unlimited ammo and unlimited health cheats can also be seen used in the E3 demo version of the game. Apply the following GameShark codes to enable them.

USA version codes:

GameShark Code Effect
800A5078 0001 All Weapons
800A5074 0001 Unlimited Ammo
800A5070 0001 Unlimited Health
800A5068 0001 Unlock All Levels

EU version codes:

GameShark Code Effect
800A52F8 0001 All Weapons
800A52F4 0001 Unlimited Ammo
800A52F0 0001 Unlimited Health
800A52E8 0001 Unlock All Levels

Debug Objects

JFG-Debugobjects1.png JFG-Debugobjects2.png JFG-Debugobjects3.png JFG-Debugobjects4.png JFG-Debugobjects5.png JFG-Debugobjects6.png

Applying the below GameShark code will display various debug objects in the current map, normally unseen. This will also display red orbs whenever you kill an enemy, display N64 logos in some cutscenes, and render all models during cutscene at once that are normally invisible.

Version GameShark Code
USA/Japan 8100E138 0000
8100E13A 102D
8100DBA8 0000
8100DBAA 702D
Europe 8100E118 0000
8100E11A 102D
8100DB88 0000
8100DB8A 702D
(Source: Original TCRF research)

Crash Debug Screen

To do:
Explain this in detail.

If the game crashes while debug mode is enabled, it will display crash debug screens. A and B change pages, R zooms in and out, C buttons allow you to view different addresses on page 2, and Z views the different memory regions on page 6.

Unused HiRes Mode

A high resolution mode appeared to have been planned at one point in development, but unfortunately, the code for the mode was never completed. As a result of being incomplete, the mode does not move objects on screen accordingly nor does it work after a level load, resulting in a crash. If you wish to see the results of the high resolution mode yourself, there are GameShark codes below to enable them. Apply the code, then reset your game if you are on a emulator.

LowRes HiRes
JFG LowRes.png JFG MediumRes.png

USA codes:

Gameshark Code Internal Name Effect
800FF384 0000 Ntsc LowRes Default 320x237 resolution.
800FF384 0090 Ntsc Widescreen Default widescreen resolution.
800FF384 00B0 Ntsc MediumRes 446x331 resolution.
800FF384 00F0 Ntsc HiResWide 446x330 widescreen resolution.
(Source: Punk7890 & SubDrag)

Unknown Map


A green and black cube found among the models used on the map screen.

(Source: Original TCRF research)

Unused Graphics

Various level editor related graphics.

A green texture with a red X and "SHOOT ME BIG BOY" written on it. Internally named SecretDoor.

JFG RocketPad.png
An unused pad with a rocket on it. Internally named BombPad.

(Source: Original TCRF research)

Unused Cutscenes

Use the map modifier code 810A323C ???? to appear in a cutscene from the below sections.



Value: 002D

A cutscene featuring a large ship not seen anywhere else in the game. This cutscene appears to be unfinished as there's no audio and it softlocks the game as soon as it's done playing.


JFG UnusedCutscene.png

Value: 00EB

An unused cutscene in Tawfret which shows a zombie ant slowly walking towards the camera. After a few seconds, the screen goes white.


Value: 018F

This is essentially the same as the used Goldwood takeoff sequence, except it plays Ichor music at low volume and the SFX is louder. The used version of this is value: 0061.


JFG UnusedCutscene2.png

Value: 0199

An unused Mizar's Palace sequence. No player is spawned in this cutscene. The game essentially softlocks.


JFG UnusedCutscene3.png

Value: 019A

An unused Mizar's Palace sequence. No player is spawned in this cutscene. The game essentially softlocks.

Unused Enemies



An unused dragonfly enemy which can only be found in the unused OTHERS test map. It's currently unknown if this enemy is still functional.

Lava Monster


An unused lava enemy which can only be found in the unused OTHERS test map. It's currently unknown if this enemy is still functional.

Butterfly Bug


A fully-functional unused drone enemy which can only be found in the unused GALAXIANS test map.

Horn Galaxian


Another fully-functional unused drone enemy found in the GALAXIANS test map.

Red Ant


An unused flying red ant only found in the unused ANT TYPES test map. It appears to be fully functional as it will shoot you if you get too close. Since the map it appears in has no AI programming, it won't move around.

Spanner Hand


A large robotic enemy which can only be found in the unused BIG BADDIES test map. When you're near the enemy, it'll fire a laser which harms you. Oddly, it makes a rooster crowing sound which was most likely just a placeholder.

Unused Weapon

An unused weapon can be found left within the game. The projectile consists of one green bullet, however, when hitting a wall it will branch off into three extra projectiles. This goes on for about four seconds until it disappears. When a direct initial shot hits an ant, they will explode. The gun has no special icon or sound. The sound is that of a pistol shot, and the icon is of the Grenade weapon. Apply the following GameShark codes to have the weapon:

Add to Juno's Inventory (must have at least 2 weapons first):

Version GameShark code
USA 811E6214 0064
Kiosk 811E36F4 0064

Or replace Juno's current weapon with it:

Version GameShark code
USA 811E6214 0064
801E6252 000F
Kiosk 811E36F4 0064
801E3732 000F
(Source: Original TCRF research)

Unused Sounds

Instrument Samples

Two drum type instruments which were used in GoldenEye and Perfect Dark can be heard here.

An unused jet pack sound which was only used in Blast Corps can be heard here.

(Source: Original TCRF research)


A rooster crowing. This sound is only used by an unused enemy.

Unused Music

Three unused songs remain in the game.

You can apply the following GameShark code to listen to them in-game.

Version GameShark code
USA 800A0698 00??
EU 800A0908 00??

Where "??" should equal one of the following values:

36 Unused song 1
3F Unused song 2
2C Unused song 3

The third song was originally value 4F in the kiosk demo version of this game. The first two unused songs remain the same.

Unused Song 1

Unused Song 2

Unused Song 3

Unused song 3 sounds like it might have been used in Tawfret at one point.

(Source: Original TCRF research)

Out Of Bounds Boxes


In the second area of Cerulean, there are a couple of small blue boxes placed just outside of the map. It's possible to see these in-game by clipping the camera through the wall. These boxes don't appear anywhere else in the game.

(Source: [1])

Anti Piracy

On bootup, the game checks for the correct CIC lockout chip. NTSC copies check for a CIC-NUS-6105 and PAL copies check for a CIC-NUS-7105. This check is done by using the challenge-response feature of the 6105/7105. If the check fails, the game will enable a couple of anti-piracy features:

You won't be able to use any of your weapons including the fish food. Pressing Z will make your character hold their weapon up, but they won't fire anything which makes it impossible to get past the first life force door in Goldwood as it requires you to shoot down three enemies.

The second anti-piracy feature is that you won't be able to run at full speed anymore, only a very slow walk. This feature only affects Juno though as Vela and Lupus are still able to run at full speed.

Most backup devices usually piggyback off of another cartridge containing a 6102 or 7101 lockout chip which activates the anti piracy function.

Internal Filename Oddities

  • Amusingly, the boss in Tawfret is internally named FatBob.
  • The Shocker weapon is internally named ShrinkBeam suggesting that at one point during development it may have shrunk enemies instead of electrocuting them.
  • King Jeff, Magnus, and Midge are internally named MrHints1, MrHints2, and MrHints3 respectively.
  • Some objects are named after developers.
    • The large alien that appears in Eschebone and it's tongue are named stevegrub and stevetung respectively.
    • The sliding doors found throughout SS Anubis are named bryan_door.
  • The Spacestation and Walkway levels are internally named Steve Sewer and Lee Walkway respectively.
  • One of the rooms in Ichor is internally named MilitaryBase JetPac Room even though you can't use the jet pack in this particular room.
(Source: Original TCRF research)

Regional Differences

North America/Europe Japan
JFG USAengfont.png JFG JPNengfont.png
  • The English font is different and larger in the Japanese version.
North America/Europe Japan
JetForceGeminiTitlescreen.png JFG JPNtitle.png
  • The game's logo was changed in the Japanese version.
North America/Europe Japan
JFG USAdebug.png JFG JPNdebug.png
  • The debug display is less informative in the Japanese version; however, the code to enable it remains the same.
North America/Europe Japan
JFG USAtxticons.png JFG JPNtxticons.png
  • The button icons have letters on them in the Japanese version.
North America/Europe Japan
JFG USAsfxicon.png JFG JPNseicon.png
  • The SFX icon in the options menu was changed to SE in the Japanese version.

Other Differences

North America/Europe Japan
JFG-nameentryus.png JFG-nameentryjp.png
  • The American and European versions allow up to 16 letters for a save file name, while the Japanese version allows only up to 8 letters.
    • In the international versions, pressing B will always exit the name entry keyboard. This was changed in the Japanese version so that B acts as backspace if there are any characters currently typed in.
North America/Europe Japan
JFG-tribalbloodus.png JFG-tribalbloodjp.png
  • The Tribal's blood is red in the American and European versions and blue in the Japanese version.
  • Certain cutscenes can now be skipped in the Japanese version, such as the cutscenes for when the characters' ship descends on a planet.
  • The Japanese version no longer auto saves after getting a new record in a level.
North America/Europe Japan
JFG-spacestationus.png JFG-spacestationjp.png
  • The Spacestation level was renamed to UFO.
    • The level names were also moved from the right side to below and the extra numbers were removed.
North America/Europe Japan
JFG-gametimeus.png JFG-gametimejp.png
  • The Japanese version displays seconds on the game time in the file select screen.
North America/Europe Japan
JFG-resultsus.png JFG-resultsjp.png
  • The Japanese version no longer displays milliseconds in the game timer upon completing a level.
  • When low on health, the indicator will flash in the Japanese version.
  • In the international versions, enemy heads can be collected to unlock cheats. Enemy heads can't be collected in the Japanese version, so the first two cheats are unlocked at the start. The third cheat, ants as pants, was removed.
North America/Europe Japan
JFG-regionnameus.png JFG-regionnamejp.png
  • Each region in a level has a unique name in the international version. In the Japanese version, the regions are simply named Zone 1, 2, 3, etc.

Rare Replay Differences

To do:
Check for more differences.
  • The Nintendo logo is no longer displayed on startup.
  • All N64 controller prompts were replaced with Xbox controller prompts.
  • The noise effect that appears when Lupus uses the night vision goggles is no longer present.
  • All mentions of Nintendo were removed from the credits.