I think most of my comments were covered by other commenters, but I'll lay it all out here anyway. Full Disclosure, I wasn't able to get very far.
Overall I think there's a lot of fun stuff here and I'd love to play an updated version if you decide to keep working on it and submitting to a future SMVM.
Story: I liked the overall vibe here but I think would have appreciated a bit more "show" rather then "tell". the intro cutscene was pretty cool but I think it over-explained some things and could have been reduced to about 25% of the current length. then you could sprinkle in more of the color-commentary later on. I also would have appreciated the game only triggering a cutscene a single time per 'life' so I didn't have to hear about the red fog power so many times :)
Overall there's a lot of Lore here and it really makes the world feel unique and somewhat mysterious.
Gameplay: The controls felt a bit floaty and I felt myself wanting to 'feel' more in the combat. The sprites changed colors when getting hit or hitting monsters, but for some reason this wasn't enough for me to really feel like I was engaged in the fight. I think SFX would help and maybe some sort of 'force' when sprites are hit to push them back or stop momentum.
I think adding some screen transitions would be helpful. Same for music transitions. maybe fade the old track out as you fade the new track in.
I had a pretty inconsistent experience with jumping. Sometimes I could jump really high and sometimes I could barely get half as much airtime. I thought maybe it was momentum based, but that didn't seem to be it. Also, I think adding some sort of 'coyote' time when walking off ledges would be very helpful. The edges of the ledges are often lush grass, which sometimes makes it difficult to know where the true end is so coyote time (allowing the player to not start falling immediately after walking off a ledge) could be helpful to provide a bit more forgiveness for some of the jumps).
Had one situation where I left the game for about 5 minutes then came back and died then when it respawned, the game was entirely black. I managed to get it back by (I think) trying to walk out of one level into the next then back). There was another situation where pressing the dash button always respawned me back to level 1 (with the vertical column of light scene playing like I was respawning again). I was unable to reproduce both of these issues.
In the High Boots level, I couldn't read the sign in the bottom left since it was behind a parallaxing tree.
Minor gripe that when I would jump on the roof in the starting locations and leave the screen, I would spawn in the new screen at ground level, not on the roof (from a gamedev perspective I get why this is happening but as a player I wanted to still be on the roof :)).
The intro cutscene said that I was brought back but part of the contract was to give all of the Souls to the demon who brought me back. Maybe I never made it far enough but I wasn't able to figure out if Souls were something that was actually part of the gameplay? or if that was just flavor text.
After finding the High Jump boots, I was not able to figure out how to exit that level. I kept trying to make the jump to the far right to get out of the level but it didn't seem like the boots were making my jump higher and I wasn't able to leave on the left. There was another jump in the top middle that I tried to get to but it also didn't work. I'm hoping to try to play again sometime to try this out some more but I'm open to tips (either here or you can DM me on discord).
I agree that the insta-death is pretty tough, but I think with maybe some intermediate checkpoints or not always playing the voiceovers every time could help that feel less frustrating.
Graphics: really solid! great style! I love how this game has a very distinct feel to it that I don't think I've seen very often. The player art is great and I really like the parallaxing effects.
Minor gripes that some of the button text doesn't quite work when everything else is so stylized, but I'm assuming that's probably due to the one month limit. Hopefully something could be addressed if you decide to keep updating the game.
Audio: I loved how there were multiple music tracks for the various areas and they all felt distinct yet connected. See my comment above on maybe considering some better music transitions between levels.
You really need some SFX though (which I think has been discussed below). When I first killed a skelly I didn't really realize the stuff it spit out were actually pickups and not just random graphic bits that it dropped. I suspected they were pickups and when I finally stared at my HP/Stamina meters while picking them up and seeing them change, it confirmed it, but I think it would have been more satisfying to hear some sort of audio cue when picking them up. Similarly with the combat, having some sort of 'hit the enemy' sfx and 'enemy dead' sfx would have helped the combat feel.
I did like the player sfx (walking, jumping, dash, fight) so I think you are on the right track there.
Enjoyment:
I had fun playing but due to dying a bunch and the handful of glitches and having to sit through the cutscenes (after restarting the exe, or in the red fog level), I had a hard time grinding through the learning curve to make it very far. However that said, I really really want to know more about the story and this player. What is the ulterior motive of the demon who brought the player back to life? what other sorts of moves will the player learn? etc. So I hope you keep working on this and I'll keep an eye on your studio and this game in case you make an update for a future SMVM.