This is really fun, I'll be sure to play the sequel when it comes out. :3
Anyway, maybe you should have the bullets shooting bullets shooting bullets in a bonus level or a later survival wave, or something in the sequel. It'd be challenging, but probably fun too.
If lance is kinda rusty with his violin and he played a three violin song with just one violin, i wonder what he could do when hes NOT rusty on the violin 0_o