Awesome concept! A bullet hell tower defense is a great idea and I was able to beat wave 20 (the last one), but there are some balancing issues. You can snowball money pretty hard (start with atms, but switch to shooting the cat statue once you get spread and burst). Also burst and spread are downgrades for atms because they lower your damage per shot and cause more lag, but the run I skipped these upgrades I made it to the end without any lag. Also investment mode is useless later on when you make literally 100x more money shooting the statue. After like round 9 I was able to get basically infinite money and was killing every enemy before they could be seen soon after, making the rest of the game trivial.