I'd perfer a villain that doesn't have a definite form. Think about Link's Awakening; the final boss was the nightmare, but if you think of it, the entire dream was the main villain. It was a false world that consumed both Link and the Wind Fish. So, in reality, you are really fighting against the entire world/dream of Koholint Island. I think it makes a far more engading "villain", if you can even call it that, than Ganon, Vaati, Dark Link, or any other Zelda cliche.

On a side note, the Twilight was interesting in Twilight Princess because, originally, I thought that the Twilight was an entity of its own that couldn't be controlled by any real organism. I felt disappointed when I found out that Zant (or Ganondorf) were in complete control of the Twilight because it took a lot away from the mystery and evil of the Twilight. I wouldn't mind Nintendo bringing back an idea similar to the Twilight or a nightmare, but I'd really like them to build on the idea. Link vs. the universe seems far more engaging than Link vs. another cliche Ganon-like baddie.

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