Catchy tunes! Was fun to play through.
One thing I'd have liked is if the different attacks had to be used in different solutions. E.g. a monster that gets only hit by a certain attack.
This was the best game I played so far! Played a few times until I got 87 loops. The core loop of killing zombies and staying alive was fun, but I think the upgrades are a bit confusing. There are cards that seem pretty bad and some that are OK. The ones that take HP seem too difficult. Maybe you could try making cards that switch guns and adds combo abilities (e.g. a gun that makes the next shot 10x strength). But again, well done!
Somehow I had to zoom out to see the whole game. Gameplay: it took me a while to figure out what's going on. I think some iterations on tutorial would help. Once I figured out you can reply each ghost separately I started really enjoying the game. The main criticism I have is that platforming "in your mind" is not ideal for me. I was stuck at the level below because I had to time the platforms blindly with just input. Ideally the puzzle would only require hold a key until you hit a wall so you can solve the puzzle a bit more reliably without invisible platforming :) As an alternative, maybe the player could play the ghosts before dying 3 times?

I could work around the resolution issue by zooming out in the Chrome zoom settings to 50%, then using pinch to zoom on my Mac to make it larger again.
Super cool idea. I think it is unique and creative. To be honest I was a bit frustrated by having to trial and error the timing and gave up at some point. But maybe with some physics tweaks and level design maybe the game could feel less hard :)
Small feedback on the UI: I often didn't know what button was active, so I restarted instead of continuing the game. If you are still trying to play and the game is over you may accidentally press the right key and it will move to the restart button, even if I beat the level.