Credits Song for My Death is royalty free?
The game is very simple and I was a little confused on what I was supposed to do, but I dig the aesthetics and appreciate what you were going for.
The abrupt music cuts really caught me off guard, though. A quick tip for that: you can use a lowpass filter on your music bus and decrease its cutoff frequency (or just enable it) when the upgrade screen shows up to create a muffled effect. I recommend taking a look at Godot's AudioServer documentation.
Overall, good entry. You did a nice job :)