This is cute! I love the cat sprite a lot, especially the little expressions it makes! I also like the idea of having to shrink enemies to beat them. The beam moving around enemies also looks very nice. Good job!
Two pieces of criticism:
1) It was a bit hard for me to see the dark red enemies against the dark grey background. I'm admittedly a little colourblind, but I'd recommend creating a bit more contrast!
2) It didn't feel very fair when an enemy would damage me by spawning from a wall that I happened to be standing near. I recommend making enemies spawn away from the player, or spawning them directly in the play area.