Just an idea..

Could it be possible, though hacking, to alternate the pull of gravity? Like, flip the map upside-down or some such. I 'dunno. Good idea? Possible? Complete rubbish?

 

Good idea? Possible?

Not really. Yes. Thar you go, all the info you ever needed.
knock yourself oot.

 

Awesome, but first, I'm going to learn two-cents about Assembly.

 

Just tried this. Leads to numerous difficulties as when you are on the ceiling, you are not on the ground (Meaning it still registers you as airborne, so you can't interact with things or jump)

Changing the pull of gravity is trivial; fixing the consequences is a little more challenging.

 

It might secretly be easier if, instead of changing the pull of gravity, you changed everything else. Meaning you flip the map upside down, change the y coordinates of all objects (i.e. entities, bullets, the player, camera focus position) so that they are flipped. Presumably the graphics are buffered before being rendered to the screen, otherwise there would be horrible flicker. You'd then have to flip the buffered graphics right before the non-gameplay objects (i.e. text box, item interface, thingy in the upper left corner with weapons and hp/xp bars, and boss hp bar) are drawn to the graphics buffer, so that they appear right side up, and everything else appears upside down.

Though admittedly, even that would be rather challenging, and if there is a relatively easy way to alter the player's behavior so that they can jump/interact on the ceiling, that might work better.