>>712522706
>is there a super boss of sort? Is it locked behind the Lunatic difficulty
Yes, there is a superboss. No, it is not locked behind Lunatic difficulty and you can do it in any difficulty.
> I skipped the whole Encore shit because I completely forgot about it. Is it 100 floors or something?
No, it's an extra dungeon that gives you jump-in sessions, more outfits, and a new "side story".
>I vaguely remember there’s another ending only obtainable if you maxed out all support points including the unplayable characters like Barry. Is this correct?
Yes, there is another ending if you complete everyone's side stories. You also have to talk with everyone in the epilogue so don't forget that.