...and if you are a normal person, you didn't finish it right away. It's really challenging and fun so give it a couple of tries before you read this guide. When you get frustrated to the point of madness, you may return here and read up on some strategies about the battle. BUT NOT A MOMENT BEFORE THAT!

There were no great guides for this battle when I tried to finish it. So I got stuck and frustrated. Somehow I managed to complete it with a little bit of luck at the end. I had worked up a tactic for the first six spins but always failed at the seventh.After destroying the square, there are only seven spins before completion. I had no idea that I was so extremely close and it all felt really random after the sixth spin, so I started guessing. I got lucky with the last one and completed the game. Afterwards I read a little in the forums and found a simple and clean solution to the problem. This strategy was similar to mine and nicely written so I'm just going to quote it:

Originally posted by poly:

I found a pattern that works on the third part of the third boss...

For the square, keep choosing the DOWN key, so that you kill it with a 180.
Then, note which of the static arrows is pointing at you before it rotates.
There are seven in the final wave, and you just have to choose the key for:

1. At (point at the killer static arrow, before it rotates)
2. At
3. Away (180 from the killer static arrow, before it rotates)
4. At
5. At
6. At
7. Away

Whew!
This way my focus is on that simple pattern of 7, without keeping track of anything else.

This should give you an edge in the third boss battle. I played again against the third boss with this strategy just to try it out, and it worked like a charm. Finished it on the first try. It worked extremely well. Thanks poly for posting these instructions and tips. You da real MVP.