Perhaps a new boss for a little refresh and extra challenge might come in the form of Skrok, a large bird, or Draco, a dragon, which acts very similarly to a Jet enemy, but has much more health.

It's features might include:
A speed dash, where it becomes more vulnerable to attack, but travels much faster.
It might breathe fire on frozen enemies from above, damaging them slightly, but unfreezing them for a short time.
It might pick up weaker enemies and move it forward faster than it could go on its own, though this would slow the boss down.
A wind gust, similar to the Gust ability, but to push the enemies forward slightly, which it might only be able to do once or twice per iteration

Or, possibly an individual wing health system, where the entire boss would start out fast, but if you can cripple the wing(s) it slows down dramatically

I know this won't make it far, but I figured I could pitch the idea, take care Devs!