This was amazing! Very creative and the art?! All made for the jam? Wow!
I have a few ideas for balancing:
a) being able to shake the window as much as you want makes the mechanic a bit pointless - have there be some penalty for abusing it or only allow a small amount of time for shaking.
b) shield stacking is completely OP. Don't allow stacking and it's fine. Have some enemies do 2 hearts of damage and it's challenging.
Thoroughly enjoyable experience, thank you. Best one so far!