|It was Sephiroth with the katana in the Dining Room. BAM|
MatPat takes a look at a different game in each video and much to my enjoyment, he deeply analyzed a scene (albeit a sad one) from a Final Fantasy game. All of us know that in Final Fantasy VII, Aerith (or Aeris, a mistranslation) was impaled by Sephiroth's incredibly long katana, but MatPat proposes another killer of the Ancient, which is how he ends all of his videos; that is, by proposing a theory.
MatPat looks at the scene of Aerith's death very analytically; dissecting it in a true scholarly fashion. I suggest you watch the video to see how it plays out, because Mat's findings just might shock you.
MatPat's page on The Punk Effect