I was thinking about the scene from the trailer with the WoL stumbling alone in the wasteland... and I'm going to predict that this is the Lv78 trial.

Something happens in the Lv77 dungeon (because LvX7 dungeons tend to end badly for certain comrades) and we're isolated from the other Scions. Maybe they're trapped or apparently killed and/or their souls finally snap back into their bodies on the Source. Anyway.

So stuff happens, we're on our own now with a taunting gremlin, and Innocence (probably a recurring appearance before this point) attacks. Cue the theoretically-solo trial fight.