The game is amazingly good. The design was well-thought-out, and the mechanics were greatly polished. My only criticism isn't really a mistake on your part, but something that could improve the web build.
The game lags when particles are first summoned. All you need to do is use CPUParticles2D when the game is being played on web (you can check that with OS.get_name(), as far as I remember). And you can tell the game to use GPU/CPU particles depending on the platform. You can have an if statement that enables the CPUParticles2D and disables the GPU ones when the game is a web build. It's really useful for game jams. Last year I had the same issue and I fixed it this way (and I actually suggested it for your game last year too).