Disclaimer I also haven’t fought the final boss.

I wouldn’t count on the Demon King being a terrible difficult fight. You have to remember that it’s a storyline quest, so it has to be achievable by the least common denominator. If you really want a challenge, you should explore the depths under the southwest region of Hyrule Field ;)

I’m not sure I understand what you’re saying. Did you mean that child comments are not federated?