Like Eternity, the Living Tribunal is not a villain per say, but if it decides to destroy the Earth for the greater good, it will do so without hesitation.
Speaking of elaborate sci-fi that’s hard to digest, how about the Living Tribunal?
Maybe Thanos’ actions throw the cosmic balance out of whack, and the Living Tribunal arrives to wipe the slate clean, destroying everything in the process?
However, the Living Tribunal might be too powerful a foe to defeat believably.