Here's a different MMX glitch idea that also goes into the grey area.
There are three passwords that completely malfunction when put in:
2226-5352-8868
7443-2241-1221
5778-8422-3577
Instead of loading a game, it gives the "incorrect password" buzzer sound, then proceeds to start a new game
without completely initializing memory. The end result is a locked-up game because X's max health is zero.
The key aspect of this glitch is the fact that memory is not completely initialized for a new game. How can that be leveraged? Let the attract mode demo load. Yes, if you wait long enough at the title scree, an attract mode demo begins to play, showing some subpar gameplay of a fully-powered X, demoing all the weapons and their charged versions. The demo just has to be
loaded, pressing start to end it and go back to the menu is all you need. So, if you use a glitch password (the second one seems to be the fastest to input) after making the RAM "dirty", you can then start a new game... with all the weapons, heart tanks, and sub tanks.
Armor upgrades can't be obtained this way, and using this method seems to invalidate any access to the Hadouken. The intro stage becomes a lot faster (use Storm Eagle's weapon on the bee copter miniboss, with a well-timed jump, to skip the whole "falling into a pit then climb out" sequence) and slower. (You have max HP, a means to get that lowered drastically before Vile is needed.)
But after the intro stage, the fortress stages are immediately available. That's because having a weapon means the Maverick boss was defeated. It also means being able to skip the mandatory Leg part in Chill Penguin's stage, which may or may not be a good thing.
The glitch works on the JP and US (1.0, 1.1) ROMs, and can be performed on real hardware. But it's still a bit of a grey area due to the use of the password screen.
Here's a video of the glitch in action.
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