Okay. I played trough it, but I have to say that that third level made me absolutely hate the game. Probably took me 10 restarts and once I even accidentally reloaded the whole page due to an angry click. The mark/block leaving mechanic just didn't feel well implemented and I could never judge where it would appear, especially so in the third level where the platforms were tiny. The collision of those blocks also felt way off especially when trying to do a tricky jump from below a block, in a question mark pattern. I also felt like I was dying to the spikes when I should've been safe, which added to my frustration.
Nice retro aesthetic, but the scanline shader is a bit extreme especially vertically. I'm really sorry to say this, but it was fun to watch, not fun to play.
Edit (after getting a cup of tea and calming down a bit). For some reason platformers, especially more hardcore ones really get under my skin. I might just not like the genre.