Spock seems rather dimwitted at the end of this episode. He could either stun both "Kirks" or ask them questions that only the real Kirk would know from their private experiences. Instead he lets Kirk get into a fistfight with his double.
Garth can apparently shapeshift clothes (or he doesn't wear clothes and the "clothing" we see is shapeshifted skin). But...when Garth changes from Cory to Garth, a working phaser appears at his holster - where'd it come from? Or how'd he create it?
Tholian Web" it's stated there has never been a mutiny
in Starfleet, but this episode establishes that Garth's crew mutinied
against him several years previous.