Wow, thank you for the in depth writeup! We had a weird issue with hitboxes in our html version, so the spikes and destructible blocks had bigger hitboxes than expected. They work better in the downloadable version, I'm not 100% sure why...
As far as the skills go, you do unlock one after every level. you can choose which one to use with the select button, and you can use it by pressing up+attack. Unfortunately, I ran out of development time, so I never got around to teaching the player all of the mechanics. One of the abilities helps you get past destructible blocks :)
The password system does function in the downloadable version, but in the web version the "accept" button double triggers, so it goes to the password page, then it accepts a password of all zeroes with one keypress.
I'll look into the game widow sizing, I neglected to setup the linux configuration during the jam, but it should be a simple fix!
Thanks so much for playing, and leaving such useful feedback! We'll be posting a bunch of fixes post jam :)