this is the stuff
datamined about the Terra Wars collab (which was marked as Terra Battle 2 before):
"Noctis, who has been having a nightmare opens his eyes. Can see a daemon that appears like a Grim Reaper. It is impossible to differentiate whether this is a dream, or reality. Noctis collapses/faints. Sara appears, protecting Noctis from the daemon."
Sara's sword (you can see it in the trailer)
the ruins are similar to solheim structures you find in the main game, so either they are reusing assets for the sake of it or they'll tie in something lore-wise / both.