Was thinking on this after running it multiple times.

1) Personal replay system to understand what happened when you died. Like snapshot the last 5-10 seconds before you were killed, and have the ability to replay that. Also, show hidden target areas of the attacks when doing the replay. It will help a lot.

2) A checkbox progress meter based on key mechanics the boss does. This is more of a personal record so you know what specific mechanic you've survived past. It's not perfect, but I'd love to be able to know how many more checkboxes there are before the enrage hits on each fight. They could even have ??? next to the ones you haven't seen yet.

Was trying to think of other things but those two would be "nice to haves". Not sure what else would be missing.