Really fun game! It crashed on me during my first playthrough (not sure why), and the first time I played it, I was not sure how to select the enemies for the wave, had to spam click everything I see to figure it out. Otherwise, its a pretty fun game, and my favorite strategy is just sending as many purple triangles as I can to rush the player!
One cool thing that you can maybe explore if you ever want to expand on this game is swarms using flocking AI. This could allow for enemies with what looks like minions following them around, either protecting them, or helping to deal more damage as you run head first into them.