Extending the demo: Street Fighter Zero 2

Unlocking Street Fighter Zero 2 Taikenban, a prototype demo with some hidden secrets.

Intro

Street Fighter Zero 2 Taikenban is a very generous demo disc. It lets you play Arcade and Versus mode as any character without any particular time limit. It doesn’t give you everything, however. The bonus illustrations are missing, and the Training and Survival modes aren’t playable.

Mode select in the demo versus Mode select in the final game.

…or are they? You guessed it; this is another one of those demo discs with a prototype build of the full game on it. You can change a few bytes to get access to the missing modes.

Here are some Action Replay codes that do the trick:

060276b6 0009
06027726 0009

Or you can use this patch from SegaXtreme.

This article will describe how to access the hidden parts of this demo disc, and will show off some differences between it and the final version of the game.

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Accessing the hidden modes

The demo version’s Mode select screen seems to have spaces for the missing Training and Survival modes. So it’s a good place to start looking around. I did a diff on some memory snapshots to find that the cursor position is stored at 0605c68c.

It’s 01 when Arcade mode is highlighted, 02 when Versus mode is highlighted, and then skips down to 05 when Option is highlighted. We can set a write breakpoint for the cursor address to see what’s making it skip:

We can just nullify that last line to prevent the jump from 03 to 05. There’s a similar jump when going up that we can patch out.

Now the missing menu items pop into existence when we navigate to them!

Training mode stops being hidden when you highlight it.

This lets us play Training mode and Survival mode. And there’s a surprise: Arcade mode and Versus mode use text-based menus for character selection in this demo:

Left: Arcade mode character select in the demo. Right: Two player versus mode in the demo.

But Training mode uses character select screen that looks a lot like the final version’s! The only difference seems to be that the Training mode text in the upper-right corner is missing.

Left: Training mode character select in the demo. Right: The final version.

The actual training mode has a unique feature: extra options in the pause menu.

Survival mode is similar: it uses a graphical character select screen. What’s the deal? I assumed the text based one was used because the full one wasn’t done yet. But that’s clearly not the case.

Left: Training mode character select in the demo. Right: The final version.

How about the Illustrations mode? The cursor wraps around from 06 to 01 when we go down from Options. We can watch the writes again to see why this is happening. Here’s some pseudo-Python adapted from the assembly:

if val_0600cc35 == 0:
    cursor_position += 1
    if cursor_position > 6:
        cursor_position = 1
else:
    cursor_position += 1
    if cursor_position > 7:
        cursor_position = 1

Aha - the value at address 0600cc35 controls whether we can go past 06. It’s normally 00, so if we set it to 01…

Left: “Omake” mode in the demo. Right: “Illustrations” mode in the final.

This build calls it Omake mode instead of Illustrations mode - neat. Alas, it doesn’t work! Selecting it takes you back to the title screen.

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Build comparisons

This demo build is dated 1996-07-24. The final game was built on 1996-08-18. There’s a prototype on Hidden Palace from 1996-08-06. I checked, and that prototype still has some of the demo’s features:

• It still has Sample on the title screen

• It still calls Illustrations mode Omake

• The Omake mode still doesn’t work

• It doesn’t have Training mode or Sample mode on the character select screens

However, it doesn’t use the text-based menus for Arcade or Versus modes.

All three builds have different renditions of the intro. Here’s a side-by-side-by-side comparison:

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Outro

Tell me what else you find that’s interesting in this prototype build! Also, be sure to point me at other demos or games that you think might have hidden extras.

As usual, feel free and encouraged to put any information on this site (including screenshots and videos) on your favorite reference site - The Cutting Room Floor, Hidden Palace, etc.