About Vecna I published something in Ravenloft reddit, and I have thought about to publish it here too.
Metaplot continued: Venca vs Dark Powers.
Vecna wants revenge against the Dark Powers, and he has a plan. He helped the dark lord Azalin Rex to try escape... and the success was partial. This caused the fragmentation of the Core. The previous dark lord of Falkovnia was killed by a time-traveler, causing an almost time paradox. But Azalin Rex isn't really free but his spark is within Hazlik.
Other ruse to cause more troubles is catching members of the cult of Tharizdun, the Elder Elemental Eye from the different places in the D&D multiverse, using the demiplane like the cosmic version of a nuclear graveyard. These are "creating" "abyssal genasies", and they can use elemental creatures against undead monsters.
There is a secret planar gate between the old Falkovnia, ruled by Vlad Drakov, and the new, the zombie apocalypse rule by Vladeska Drakov. There are also other secret planar gates to Innistrad.
The old "Core" hasn't disappeared really, but without their previous dark lords, and the control by the dark powers is weaker. There are more human(oid) population, but also more supernatural predators, because now it is a "bigger hunt zone".