Under the microscope: Congo the Movie — The Lost City of Zinj (Saturn)

No popcorn box to hide behind this time

Congo the Movie: The Lost City of Zinj is a Doom-like FPS that’s set in the world of the 1995 film Congo. It doesn’t use the movie characters or scenes, however — it’s an original story with its own video clips.

As of this writing, none of the cheat sites list any codes for this game. That’s a shame, since it’s very difficult. I am rectifying the situation in this article: I found several previously unreported cheat codes that make the game much easier to play:

• Level select

• Credits

• Movies

• Unlimited health

• Unlimited ammunition

• Level skip

• Show coordinates

Details on the codes and the reverse engineering that found them are below!

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Level select

The first three cheat codes are entered at the mode select screen:

Begin by holding Start. While you’re doing that, put in this sequence:

(Holding Start) Right, A, Down, Y, Left, A, Y

The level select screen should appear:

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Credits

Enter this sequence at the mode select screen while holding Start:

(Holding Start) Z, A, Up, Y, C, R, Right, Left

The credits will start playing if you got it right:

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Show movies

Enter this sequence at the title screen while holding Start:

(Holding Start) Down, Right, Right, A, L, L, R, Right, Right, L, Down

The FMV clips will start playing:

You can press Start to skip the clip you’re watching.

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Unlimited health

The next three cheat codes are entered during gameplay. Press and hold Start to begin - you’ll see the Status screen appear:

Keep holding Start while entering this sequence:

(Holding Start) L, A, R, C, Right, Up, Y

You’ll no longer take damage from enemies, and your health will be set to 100 after your next injury:

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Unlimited ammunition

Press and hold Start during gameplay. Keep holding it while entering this sequence:

(Holding Start) B, L, A, Z, Right, A, Left, A, Y

Your ammunition will not decrease when you fire your weapons:

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Complete current level

Press and hold Start during gameplay. Keep holding it while entering this sequence:

(Holding Start) Down, Right, Left, Right, R, R, A, C, Right

The level will end and the results screen will appear. Note that you won’t get credit for any diamonds you didn’t find:

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Show coordinates and more

Press and hold Start during gameplay. Keep holding it while entering this sequence:

(Holding Start) Y, Right, Down, L, A, R, R, Y

You’ll see coordinates on the Status screen after this:

Also, enemies will immediately disappear after you kill them. They won’t hang around waiting around for a double tap:

This code might do other subtle things too, but I couldn’t really tell. Let me know if you spot additional effects!

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Technical details

One of the first things I do when I’m mapping out how a game works is to label where it stores input data. I usually find this by diffing memory snapshots with RALibetro’s Memory Inspector (see this article).

Congo stores the most recently pressed button at address 06085974. I set a read breakpoint for that address in Mednafen’s debugger to find what buttons the game is looking for. This led me to the function at 06010af0, which runs when you’re on the title screen. Its logic looks like this:

def handle_title_screen_cheats(pressed_button, holding_start):
    if not holding_start:
        cheat_counter_1, cheat_counter_2, cheat_counter = 0, 0, 0
    else:
        if pressed_button == cheat_1_buttons[cheat_counter_1]:
            cheat_counter_1 += 1
        if pressed_button == cheat_2_buttons[cheat_counter_2]:
            cheat_counter_2 += 1
        if pressed_button == cheat_3_buttons[cheat_counter_3]:
            cheat_counter_3 += 1

    if cheat_counter_1 == 7:
        return 1
    if cheat_counter_2 == 7:
        return 2
    if cheat_counter_3 == 7:
        return 3
    return 0

The pause screen calls a very similar function at 0601086c. The cheat code button patterns are stored starting at 060628d8.

The unlimited health and unlimited ammunition cheats can be expressed simply as Action Replay codes:

36062048 0001  # Unlimited health
36062049 0001  # Unlimited ammunition

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Outro

For more on Congo, see Peter Malek’s 2020 article on the game, the material that inspired it, and more.

For more cheat code discoveries, see my archive. Which other games should I be checking out? Tell me in the comments.

Logo by Ashlyn Anstee