Glad it was easier to comprehend this time!
I'll need to emphasize more that Brace spends a reaction. The main reason for that cost is that it would be guaranteed damage in a lot of circumstances if it didn't. It's supposed to be a real decision whether you use that (to keep them very safe and have a lot of block next turn if they get ignored) or Get Ready! (if you want reactions)
Commit greys out if you have fewer than two characters who are on the board and not on exits. There's a tooltip that explains, but I can add something more obvious. And a lose condition if you ever have only one usable character. And maybe grey out Undo when there's nothing to undo to.
You're about halfway - there's two more phases.
Just to check if there's something you missed.
Did you feel like the boss healed a lot, or were you usually able to prevent it?
Did you understand how to summon characters onto the board, and how to move them off the board?
Please tell me how you think collisions work (without checking)