Thanks for the great feedback.
Visuals: I don't currently have plans to change the core visuals, so if there are issues I'd love to hear about them. Other bosses will have a single sprite that moves around, without animation, but that's currently the only visual update I'm working on.
Memory: I think you're right about blind kills being an issue, I hadn't really considered that because the goal is for an extended learning grind, but I can see how it would put someone off. I'll try adding some warning ! indicators and restructure some attacks that push you into bad spots.
Audio: are you specifically thinking about an on-hit sound, or are there other things you'd like to hear?