@crabowitz
The vulnerable state in the boss is that he can hit himself with lightning during the part where the cloud tracks you. I didn't include a hint because I didn't know how without treating the player like a baby, but it's good to know that it is actually hard to figure out. My goal is that every boss is beatable (even if it's hard) if you start as Whimp, so I'll work on making those options clear.
Thanks for your feedback!