Hey, this is great! I'm intentionally searching out all the metroidvanias in the GMTK jam and this one is surprisingly lengthy and even has a boss. I think the high jump mechanic should have a little more feedback to let you know it's activated (like in Mario 2, you start blinking when you've charged it enough). There was one corridor when I had four slimes and there were three spike boys and I kept dying to them; I eventually managed to cheese it by getting close enough to the slime in the wall to get him to come to me so I could warp back to the start without having to figure out how to pass that legit. I'm still not sure exactly how to defeat those enemies -- are they just jump on the head types?, because the spikey heads made me hesitant to do that.
Also, confused about the ending, I got over the east mountain and then fell into the void. Seemed a bit avant-garde to me, but I guess these slimes would rather fall until integer overflow than be stuck in a cave.
Anyway, great game. Like I said, love these metroidvanias, and this one has a lot of content and neat upgrades, which are all benefitted from the number of slimes you've joined together -- more slimes means more weight to get to more areas, more slimes means more ammo for throwing, and more slimes means a higher max charge jump.