I was recently introduced into the Mettaton Knight theory and while I don't believe it has enough right now, it pointed out things that made me realize that even if he isn't the Knight, he is suspicious.. Especially when compared to Papyrus..
A Fun Fact! Both MTT and Papyrus don't fight back on a murder run. I thought it was a fun parallel/mirror point of Undertale when I first noticed it, but now.. hmmm...















