ive got an idea for one. instead, make the arena bigger and make the upgrades lined on the bottom of the screen, that way, you can constantly play.have the screen constantly change colors and instead of that wait in the middle each level, just have it pop up in the middle of the screen for a while
try doing this. add as many balls as possible, put the attractiveness as high as possible, and swirl them in a circle for a while and they will make one little dot. then make your balls less attractive, and it should explode in a stream of em.