And I mean this resulting in complete radical changes to flora,fauna and entire ecosystems. A fourth of the Human race dying either due to exposure to more hostile and wild magical phenomena or mained and eate by flora and fauna from Equestria. specfically the everfree forest. Som humans mutating into body horror involving a nightmarish fusion btween their human and equestria counterparts.
Society and civilization is so badly disrupted by the influx of magic that it collapses and dissolves copletely once these humans gain the powers of their equestrian couterparts and abuse it and turn their powers on their own kind. wharver ruins and wreckage of cities there are is rapidly reclaimed by plant life whos growth has been accelerated by the magic as well as half of it being flora from the everfree forest. .