How did the X-Men game for Sega Genesis have its state survive a console reset?

The Sega Genesis system had a rather interesting game. X-Men (1993) was based on the popular cartoon version of the comic book series. But it had what was still one of the most unique (and unintuitive) mechanisms I've ever heard of. In the second to last level, the game asks you to "reset the computer". The strange thing about this is there's no in-game way to do this, and many people would get frustrated with the inability to progress to the game's final level. But the reset mechanism the game wants you to activate is the console's reset button

Now years after attempting, failing and just moving on to other games, I happened to find the answer. This was years ago, by the way. To reset the computer- the player had to press reset on the Sega Genesis console. Yes. I was taken aback. It felt like a slap in the face. Not only was the player supposed to think outside the game cartridge, but they were supposed to do something NO gamer in their right mind would ever think of doing for fear of losing progress in the game.
And to top it off- if you pressed it for even a fraction of a second to long, the game would do exactly that- reset the system and you'd lose your progress. So gamers were supposed to tap the reset button which brought up a screen full of numbers and then moved you on to the next level.

The reset button should clear the console's memory. How did the game manage to survive pressing the reset button AND know that that was what had happened?

Similar methods have existed and are still used.

The reset does not clear the memory, it simply resets the CPU to start running code from start vector.

All the code needs to do is to check a known piece of memory if something known exists in memory or not, to trigger an action how to proceed after startup.

Then it is up to the game progress to write something known to the special memory address or write nonsense to make sure the function is not triggered at next reset.

This was for example used in IBM PC 5150 to skip cold boot memory test. After cold boot is done, pressing CTRL-ALT-DEL writes a special word to known memory address, so the startup code knows to skip the RAM test.

Found an interesting blog entry that adds some details to the answer by Jacob Krall. The main gist is that Jacob was right, in that RAM is not cleared between resets

SGDK doesn’t clear the entire RAM on a soft reset, so that you can keep certain data like high scores and settings alive even after a reset. It would be a bit overkill to use SRAM (saving using a battery in the cartridge) just for that. Plus, you could do even more interesting things with it… Have you ever played the original X-Men game on the Mega Drive? That game had you reset your console to gain access to the final level. That obviously wouldn’t work if a soft reset deleted everything!

What differs from what Jacob noted about architecture is that apparently the Genesis could report this state to your code directly

The simplest way is to initialize everything we need reset in main() before our game loop starts. The main() function is called every time we reset the console (using a soft or hard reset), so in our case, adding a ticker = 0; before while(1) would solve our problem and set the ticker back to 0 after each reset of the emulator.

Later

If you add a parameter to main(), you can see whether the console has been reset and how

 int main(int resetType){}

When the console has just been turned on, resetType will equal 1, indicating a hard reset. But if the reset button has just been pressed, resetType will equal 0! (You can call the parameter anything you want, by the way).

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