Continuity mistake: After Marta's dance, Kirk and Spock are sitting an inch apart behind the table, then a foot apart, then an inch again and so forth every time the shot changes. (00:16:25)
Continuity mistake: As Garth brings in the chair and orders the governor's torture, the pedestal fruit bowl on the table in front of Kirk keeps moving back and forth in relation to him and to the wine pitcher. (00:22:40)
Continuity mistake: When Garth forces Kirk to kneel at his feet, Kirk's hands are extended palms down, then palms up, then palms down again as the camera angles change. (00:34:20)
Continuity mistake: When Scott orders Sulu to fire phasers to punch through the force field, the two phaser beams are diverging when they leave the ship, but converging somehow (space mirrors?) when they strike the planet. (00:41:20)
Continuity mistake: After Garth attempts to convince Mr Scott that he is Captain Kirk and to beam him up, while he is banging his fists on the floor in anger he transforms back into himself and the fly like ring on his finger breaks and slides out of shot. It's quite hard to see but it does. The next time we see Garth's hand his ring is intact yet he has not transformed himself again to repair it.
Continuity mistake: When Scotty thwarts Garth, disguised as Kirk, attempts to beam to the Enterprise using the Queen-to-Queen level three code, Kirk throws a tantrum and accidentally loosens one of his controls during his rant right before he turns back to Garth.
Suggested correction: How is that a mistake?