Some screen-shots from level three.
As you can see, these enemies have a trail effect, which helps to emphasize their speed. These enemies are in constant motion, whereas earlier enemies come to frequent stops.
I briefly tried adding a trail effect to the third boss, but because the sprite is much larger, it didn't have the same effect-- instead looking rather ugly and clunky.
I'm trying to iron out a couple of technical crinkles in the third boss. Assuming I can overcome them this week, and that the fourth and final boss is going to come together as quickly as I think it will, the game should be done by the 20th at the latest-- ten days before the deadline.