I played it for a while, but I didn't reach the end because I am bad at navigation. There is a lot of stuff in there, and I really had a fun time while playing, even if the sometimes tight jumps and instant death gave me Flash game vibes.
I'm not the first one to say it, but the big crate textbox is annoying. You should add coyote time to the jump too, because I had many death related to slipping off platforms (especially in the spike pits requiring the dash, and also the red platforms). I don't know if it's normal, but I gave up at the big crate just after the first falling platform because I pushed it against a wall and can't get to the ledge on the right if that's what I'm supposed to do.
I found a cool thing about slopes, if you dash on them you get a very cool high jump and I loved it. I also liked the section with the red platforms, woke up my nightmares about Heatman's stage I thought I got over a long time ago :P
The sections with moving platforms are a bit scary, because they are so far apart, but in the end I didn't have much trouble with them. One thing you could do also is make the dash a bit longer, and widen the first spike pit to make it obvious it's not just the player messing up their timing on the double jump.
You did all that yourself ? That's impressive, it's was definitely a lot of fun despite how unpolished it is. I wish you good luck if you plan to make an update, this game could get a lot of love if you do.