Gwydion just bugs me. He does not seem to fit within the Gothic Horror theme of the setting. He seems like more of a Cosmic Horror creature. I have to wonder what the designers were thinking when they added him in.
While Ravenloft is mostly Gothic Horror, the setting incorporates all kinds of horror, including Cosmic Horror. The domain of Blutespur was intended to be more like HP Lovecraft with its mind flayers. One could argue that Vecna and Kas don't fit the Gothic Horror model either, but in each adventure the module explains how the adventure can be scary and what themes should be brought out (Vecna and Kas represent ancient secrets and prehistoric horror). Some domains' lies in their ability to mock or twist the expectations of standard fantasy settings, like the Wildlands mocks The Lion King with its talking animals. Personally I think that Gwydion is an espy of Morgoth or Sauron in a Tolkien setting, except in this case he's an ancient evil mocking the hope that the true king will return to the throne.