Under the Microscope: Gunbird

In this edition I’m examining Gunbird, the vertical shooter from Psikyo. I found four new cheat codes for it:

• The Test mode menu.
• NoDeath mode, which makes you invincible.
• Skip mode, mode allows you to complete stages on demand.
• Pause, which enables frame advance controls.

Details are below!

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Test mode

I previously wrote about a patch that I made for Gunbird that grants access to the game’s Test mode. But I missed something when I analyzed it the first time — there’s no need for a patch, there’s a cheat code that grants access to the menu:

• Hold Start as the game is booting up. Release it once the Atlus video starts playing.
• Enter this sequence during the Atlus video: B, Left, Up, Down, B, A, A, Down.

The Test Mode Main Menu screen should pop right up:

Gunbird’s menu is sort of primitive, and its operation isn’t very intuitive. For example, to start playing with custom options, you have to:

• Use A and B to adjust the Stage Select so that it’s something other than -1.
• Do the same for at least Char1 Select.
• Navigate to Stage play and press C to load the values (this will freeze the menu for a moment), then press A.

The Sprite Test and BG Check screens are similar: they won’t work until you load the values on the main screens.

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NoDeath mode

I also found three other cheat codes. The first one enables NoDeath mode. You’ll need two controllers and possibly four hands for this:

• At the Gunbird Press Start Button screen, hold X+Y+Z on both controllers.
• Let this screen time out. The opening animation will start to play. Press Start to skip it.
• Hold X+Y+Z on both controllers again.
• Let the screen time out again. Press Start to return to it.
• Hold X+Y+Z on both controllers a third time.

The NoDeath indicator will appear if you got it right:

As the name implies, this prevents you from dying if you get hit.

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Skip mode

The next cheat code is similar:

• At the Gunbird Press Start Button screen, hold L+R on both controllers.
• Let this screen time out. The opening animation will start to play. Press Start to skip it.
• Hold L+R on both controllers again.
• Let the screen time out again. Press Start to return to it.
• Hold L+R on both controllers a third time.

The Skip indicator will appear if you got it right:

You can now press L+R during gameplay to complete the stage you’re playing.

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Pause mode

The last cheat code is a little bit different:

• Hold Start as the game is booting up. Release it once the Atlus video starts playing.
• Proceed to the Gunbird Press Start Button screen, then hold A+B+C on both controllers.

You’ll see the Pause indicator if you got it right:

During gameplay you can now hold L and press Z to pause the game and advance by one frame. Hold L and press Y to resume normal gameplay.

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Technical details

One of the first things the game does (in the function at 06019244) is check whether you’re holding start. If you are, it sets the 4 byte flag at 060afce8.

If that flag is set, then the function at 0601b0f4 checks your input against one of four sequences:

• B, Left, Up, Down, B, A, A, Down
• B, Left, Up, Y, B, C, C, A
• B, Left, Up, Up, A, Left, C, C
• B, Left, Up, Left, B, B, B, X

Any one of them will activate the test menu. If you get one of the buttons right, the counter at 060b5224 increments. When it reaches 8, the function returns 1. This changes the game’s mode to 08, which corresponds to the test menu.

When the title screen is active, the function at 06024388 is checking controller 1 and controller 2 for identical button presses. When it finds one of L+R, X+Y+Z, or A+B+C, it updates a tracker (at 060b543c).

The Skip and NoDeath logic checks the tracker three times. The Pause logic checks it once if the “held Start at boot time” flag mentioned above is set.

Here are some Action Replay codes for all three effects:

160afcee 0001 # Pause cheat
160afd06 0001 # Skip cheat
160b5422 0001 # NoDeath cheat

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Outro

You might be wondering: I also developed patches for test menus in Strikers 1945 and Sengoku Blade. Are there similar cheats for those games? Good question — come back next week for the answer!

In the meantime, check out my archive here at SHIRO! for many more hacks and cheats. And for even more retro game reverse engineering finds, check out my Rings of Saturn blog. This week it’s got details about a cheat code for the PlayStation version of Gunbird, inexplicably known as Mobile Light Force.

Many thanks to privateye for testing out the Action Replay codes above!