This guide was created to help you with the various(And often unexplainable) bugs in MM21XX.

Radioactive Roach/Other Boss problems - If entering a Boss room, most of the time Roach's, causes a black box bearing text to appear at the top of the screen and halt the game, it means you pressed F9 an odd number of times.  To fix this, press space until the box goeas away and immediately press F9 one more time to correct this.

Ocelot Bug - If entering the boss room of Ocelot makes the game crash, pressing F9 at least four times while in his stage will allow to fight him without problems.

Sigma Bug - Often times Sigma's first form will abruptly freeze up and become immortal or slide off the screen when you get him down to about three HP.  This is often triggered by Polaris' weapon or wearing him down by single shots.  If this happens, you can trigger his second form by merely pressing the "O" key on your keyboard(Although, if he slid offscreen you may have to wait a while for him to crawl back on).