more on the far realm

the far realm inherently is a threat to all of the known planes of existence. wherever aspects or creatures of the far realm populate the known planes, the immediate surroundings slowly warp from their natural state into some semblance of the far realm ("Their presence in an area infuses it with the Far Realm’s blight, and the spreading madness invites more incursions from beyond. Dungeon 194").

thralls of aberrations are affected by this far realm influence, sometimes eventually losing their sanity (kou-toa) or outright transforming into aberrations (foulspawn).