Expansion hack: Power Stone, Power Stone 2 (Dreamcast)

Access unused debug menus in Capcom's classic fighting games

In this edition:

• Power Stone for Dreamcast has a hidden debug menu that lets you test various functions, alter game parameters, and view/edit character animations.

• Power Stone 2, also for Dreamcast, has a similar menu with equally cool features.

• I’ve made patches to let you access these menus — get them from SegaXtreme:

  • Power Stone

  • Power Stone 2

This article will describe these menus and how the patches work. Here’s a video!

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Power Stone

If you analyze a memory snapshot from Power Stone, you’ll see some interesting strings (the addresses are from the NTSC-U version):

0c1535b4 " 1. INPUT TEST     "
0c1535c8 " 2. OUTPUT TEST    "
0c1535dc " 3. SOUND TEST     "
0c1535f0 " 4. COLOR TEST     "
0c153604 " 5. DOT TEST       "
0c153618 " 6. GAME DATA      "
0c15362c " 7. CONFIGURATION  "
0c153640 " 8. MEMORY CHECK   "
0c153654 " 9. GAME CHECK     "
0c153668 "10. EXIT           "

The arcade service menu, perhaps? Following the references to these strings leads to a function at 0c0d7108. That function doesn’t have any references, meaning it’s not reachable (at least as Ghidra can tell).

While Power Stone starts up, it calls a function at 0c0d7318. This branches off to the title screen handler, the mode select handler, and other frontend functions, depending on the game’s current state. I replaced the reference to that function with a reference to the unreachable one above, and…

The menu works! Most of the items have what you would expect from an arcade game service screen¹. Input Test shows you which buttons are being pressed; System Configuration alters things like number of credits per coin insertion; Color Test shows a test pattern. Dot Test doesn’t seem to do anything. Sound Test works, however.

Left: Color Test. Right: Sound Test.

But the stars of the show are Game Check > Motion Check and Game Check > Hit Edit. The former lets you test every character animation and alter the poses. The latter is similar, but shows you something like “hit boxes” and allows you to alter their configurations:

Left: Motion Check. Right: Hit Edit.

These look cooler in motion; check out the video above!

The Game Check menu has two items that don’t work — Stage Check and BG Check. However, Ending Check does work, and so does Staff Roll.

Here’s an image that was presumably made for a demo version of Power Stone. You can access it from the Ending Check menu.

I couldn’t find a way to make the Game Edit menu work alongside the normal game, alas. If you hit Exit, you’ll just bounce back into the menu. I was able to do better with the next game, however…

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Power Stone 2

Power Stone 2 works like this: the function at 0c05f7a0 gets called every time you switch modes — from the opening sequence to the title screen, from the title screen to the mode select screen, from the mode select screen to normal gameplay, etc.

If that function gets called with an argument of 03, a debug menu that looks like the one in the first game launches:

This one is less arcade-y². Motion Check is present, and it’s got more features this time:

Hit Edit also has a bunch of features. You have to use controller 2 for the menu:

Ending Check does what you would expect, as does Staff Roll:

Left: Ending Check. Right: Staff Roll.

Sound Test is similarly unsurprising, but it’s nice to have:

The Configration (sic) items are pretty interesting. The first one is pretty arcade-y, but the Country setting really will activate the Japanese menus (and the network option, which is removed in the English versions). The second one lets you activate the unlockables:

@pomegd found that the Location Test gives a “coming soon” screen after the fourth battle.

VMS Save and Net Info don’t seem to do anything.

I was able to make this game’s menu exit back to the mode select screen. The patches are:

0c05b5c2 6689 # Replace the title screen mode 0c05e84a 04e4 # Exit to the mode select screen

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Outro

Many thanks to DarthDub for testing out the patches for these games.

What other games should I be examining? Tell me in the comments!

Logo by Ashlyn Anstee

1. Note that the arcade service menu screen does look different from this one, however!

2. Ironically, this same menu does appear in the Naomi version, and even includes the Dreamcast-specific settings.