Board Thread:General Discussion/@comment-27894627-20160511021754/@comment-27907368-20160527222731

That's not a theory, that's a headcanon. Mettaton himself does not change the protagonist's soul to Yellow Mode - Alphys does this. In the Genocide Route, the Yellow SOUL Mode isn't used at all.

... I'm really confused how this can even be classified as a theory. >_>