To anybody wondering: K to shoot.
Ended up winning by guarding one crystal and standing in place from 25% to 100%. That took a while.
When I was jumping around I was missing coyote time (allowing you to jump shortly after leaving a platform, just feels a lot better) and a retry button. Always having to start the game up again after falling down by accident was a bit annoying.
As a gamejam entry it was alright. Make your next game playable in the browser, so more people play it.