Thanks! And thanks for the details! I have a bug report notepad and check them off as I go. For the shield powerup, I had planned on(and will fully implement soon) making it an actual shield you could activate for a second, which would block an enemy's attack, but then have a few seconds cooldown time to keep it interesting. I was working on the sprites for it but couldn't make anything that I was satisfied with at all and had to scrap the idea and just program it as a 50% defense bonus and move on. I had already created really cool activate/deactivate SFX for it too. I then had to nerf the final boss a bit as I had originally designed it so that it would have been nearly impossible without the shield. So many things cut for time, but that's how it goes.
As for the charged attack, the original concept was that building up a super powerful blast wave required much more energy and so he needed to stand still and focus to build up the charge. I then realized it would be nice to be able to jump up and release it to get something up higher, so I added that in. In retrospect, it may be better from a playability standpoint to be able to charge it up anywhere as long as you hold the button, no matter what else you do besides dash, as that would be kind of an energy burst in itself. But I will have to test that out and see.
As far as saving progress, I basically save powerup and boss progress to a single slot, which overwrites back to 0 if you select "Start" instead of "Continue". Checkpoints and save slots was a feature that I had to postpone until a post-jam release. I will do some more testing with that in the browser version to see if everything is going right with that. These will be needed as for the full version I am targeting 10 full biomes/levels each around as big as the one in this version.