I have some ideas for a multiplayer version of this game, but wanted to start out with a very simple prototype to test the feel and rules.
PICO-8 is a lovely way to learn game development, as the constraints guide the design decisions.
Try the combo system! Let the sound guide you, it isn’t all speed, but pacing.
PICO-8 is a virtual console.
Refactor the background grid so that effects can be passed through it
Deeper audio and more layers
Some trails for fast drops that add more punch to the feel