re: super nerdy dream
The technical explanation, which I remember from the dream: the final boss has multiple phases, and the game allows you to straight-up leave and save in the middle of the fight. The phases are tracked with a general event counter. Somehow I got past phase 1 in an unintended way that didn't increment the counter. So the counter was still inside the boss fight, thus the boss was still there when reloading.
re: super nerdy dream
But, I couldn't do any damage because upon reloading all but one of my party members were chibi-fied? I guess whatever bypassed the counter also bypassed this status effect, but on reloading a save it's based on the event counter. Apparently the remaining party member is supposed to be able to win somehow, but I either bypassed a check for some needed item, or some other important thing that's supposed to happen.