Rise of the Flayers
They have many names. Terrors of the Underdark. Mind Flayers. Monsters from the Future.
Many knowledgeable Adventurers and Scholars know that they have arrived from the future to escape destruction.
But nobody asks how they came to be. Because, whether or not they like it, even they cannot escape a Paradox. Therefore, it stands to reason that in the future, for some reason, they evolve on a world and evolve into what we fear today. They also will likely destroy the Futureborn Illithids and take over as newer terrors. All of this will be done if only to prevent a Paradox from destroying this Plane of reality. Scholars have kept this a secret, hoping that, one day, the Illithids will be purged from their world, saving them from enslavement.
Recently, in small communities in the wilderness, there have been rumors of a strange disease that quickly kills its host. It also deforms the victims, causing their lips to split down the middle and their pinky fingers to shrivel into practically nothing. These major distortions happen in just a few weeks. Some of these villages are resorting to ancient practices to cure this disease, but none seem to be working. Not permanently, at least.