The real challenge is to do this without healing, that's what I was doing at first due to a browser bug (something to do with arkenfox's settings)
And the challenge after that is a no hit run
I took me hours to do this without healing and I couldn't beat it. Once I opened the game without arkenfox I did it in 10 minutes or less.
The boss battle is pretty easy to figure out, and highly relies on not making mistakes.