Slopes are a pain--sometimes it feels like I get backwards momentum out of nowhere. I would recommend heavy workshopping of how momentum works. The ledge-grab is nice and generous and the parrot feels good to control. However, there's enough glitches and control-lag that combat feels practically impossible to get through without a hit--especially against bats. One other control-thing that I hope provides help or confirmation would be, please just give us an abrupt cut between screens, or pause the game while scrolling. Right now it feels like neither is happening, which makes traversal upwards a pain.
Also, if I understood correctly, I've now had two game-stopping glitches, and saves don't persist between sessions. I'm considering myself as having played enough to rate this honestly now, having beaten the boss on my second attempt. Before the second bug I think I might have half-collected an essential item, but the second glitch happened before I could verify, so it's hard to say. I'll be sending some screenshots to one of your team via the MVM Discord to clarify where I'm seeing these issues.
This feels like something very special in its presentation. The theming is so strong here and the ideas in its design are pretty excellent. Congratulations on giving ability-based progression that isn't all just double-jumps and dashes, for example :).
Lastly I want to echo what another commenter said here about the level design being pretty good. You almost didn't need to give the player a map for this one.
A version that addressed even the momentum consistency issues and game-stopping bugs would be a sight to see and would feel like a classic, if short, Dos game.