Dunno if this has already been speculated, but I'm wondering if the Lands Between are literally Land Between realities, and the big tree is actually akin to the Berserk tree in more than just image, but in the sense that it represents the crossing over of planes of reality. The Golden Order was the state of affairs of order between realities, order in the Lands Between, which was created by the Elden Ring (symbolized by the crossing circles and the line through them), but with the Shattering the realities are becoming distorted like in Fantasia Arc in Berserk. I'm also wondering if the red sky is actually a phase of reality warping, since it appeared in the first trailer as a thing that burned the guy who looked at it, and we saw the Valkyrie suiting up for battle, as well as a spear being driven into a big opponent. We then see it in this trailer with a giant dragon wielding lightning. Maybe the red sky indicates a particular type of reality distortion, a particular plane of existence taking dominance in the game world. But there could be other planes of existence indicated by other open world changes. Like the blue light deer boss may be an expression of a different realm crossing over. The fact it was incredibly dark and all these other little light deer were walking around beneath it may be expressing that this realm is one of darkness and blue light type magic creatures. Whereas of course the red plane of reality is one of fire and lightning.
Edit: or maybe instead of being total changes to the game world that happen cyclically it only appears from each area that things like the sky turning red consume all the other areas, because the shattering of the Golden Order just made the physical locations correspond to different realities. So you cross over into the "red sky" kingdom and it appears as if the sky over the whole of the Lands Between is red, but it only looks that way when you're in the "red sky" kingdom.
