Hey, you are the first one to talk about the boss! Good job on reaching him.
Regarding your feedback:
1) Yes, that particular safe area is badly placed in this demo. As the final game will have a more Zeldaesque open world feel, the player will be able to access safe areas in an easier way.
2) I'm a bit torn on this because I'd like to keep prompts and visual tutorials at a minimum (I'm still considering if it makes sense to have text pop out when you collect something, or a weapon gets destroyed) and let the player understand by doing (or reading the entries in the menu), but it's a valid point.
3) Yes, right now the boss main form has a different animation playing with a timer, but I guess that with a shader (like a hologram effect going on and off) it will improve the player experience.
4) This is definitely a bug, as it should show as the purple one did.
Thanks for playing the game and for this detailed feedback, I will work on some points during the jam, but some stuff will be addressed later.