Had a lot of fun messing around! I got 9 of the collectibles but at some point my progress got reset and I couldn't figure out why so I stopped playing. Once I also got "softlocked" but eventually figured out you can press R to go back to spawn, this may have been what reset my progress? But it didn't reset every time?
Anyways, here are some controls which aren't listed:
R: teleport back to spawn (may lose progress)
E: teleport back to checkpoint
B: spawn a couple projectiles of some sort which can nudge you and other players around? I wasn't able to use them in any useful way, but someone better at platforming than me could use them to reset their momentum in midair.