* DirectedByCastMember: Creator/LeonardNimoy, marking the first time a cast member directed a ''Franchise/StarTrek'' production, paving the way for future cast members like [[Film/StarTrekFirstContact Jonathan]] [[Film/StarTrekInsurrection Frakes]].
** Same can be said for [[Film/StarTrekVTheFinalFrontier Shatner]], but people tend to ignore that one.
** Shatner was, according to "Star Trek Lives," scheduled to direct the final episode of the Original Series in 1969. Unfortunately, that would have been Episode 81, and NBC sent the word down during the filming of "[[Recap/StarTrekS3E24TurnaboutIntruder Turnabout Intruder]]" that that episode, #79, would be the last.
** In his book ''I Am Spock'', Nimoy mentions that Creator/DeForestKelley kept swearing up and down that, in the scenes where [=McCoy=] converses with an unconscious Spock, Nimoy was trying to direct him through the movement and flutter of his eyelids.
* FakeRussian: In letter, but not in spirit. Chekov actually speaks Russian for the first time. Though Creator/WalterKoenig was born in America, his parents are Russian immigrants who emigrated from Lithuania.
* TheOtherDarrin: Creator/KirstieAlley loved playing Saavik (she apparently wore the ears home a number of times) and wanted to return, but apparently failed to communicate this clearly to her agent, who demanded a higher fee for her to play Saavik than Paramount was willing to pay. Paramount switched in Robin Curtis instead.
* ThrowItIn: Kirk [[PeopleFallOffChairs stumbling off the chair]] after being told [[spoiler:David was murdered]] was entirely accidental, but Leonard Nimoy felt it suited the scene, and left it in.
** To be quite exact: Shatner stumbled on a previous take, whereupon the two convened and decided that the scene should include such a gesture. The recorded take was then staged, leading to the movie we now know.
** The official Klingon language was forced to include some complex structural rules entirely because Christopher Lloyd screwed up one of his lines and it got left in the film. However, Michael Okuda realized that the mistake Lloyd made actually ''made sense'' because it was basically a contraction of what would have been excessively formal if spoken in English.
** [[Series/BattlestarGalactica2003 Edward James Olmos]] was Leonard Nimoy's preference for Kruge.
** Early scripts have the Klingons as a rogue group who commandeered a ''Romulan'' Bird of Prey.
** And earlier than that, it was supposed to be ''Romulans'', period, in Harve Bennett's treatment. Spock's role is relatively the same, except he goes feral and kills several Romulan miners when they drill for dilithium on the Genesis planet. A subplot would have also had the Vulcans threatening to secede from the Federation over the Genesis Torpedo... [[Film/StarTrek The 2009 reboot]] would have [[FromNobodyToNightmare temporally-displaced Romulan miners]] as the BigBad.
** In the novelization, Saavik and David Marcus became romantically involved (the seeds for this were planted in the [[Film/StarTrekIITheWrathOfKhan previous movie's]] novelization); this storyline was completely dropped from the films.
** In the novelization, Saavik became pregnant with Spock's kid. This, too, was dropped.
** There was some debate as to [[spoiler:who would get killed off at the end, Saavik or David Marcus. Ultimately they chose to have David make a HeroicSacrifice to atone for the damage he had done with the Genesis Project and also to balance out the return of Spock.]]
** Creator/GeneRoddenberry would have preferred it had the ''Enterprise'' just lost its saucer and not the entire thing, envisioning the movie ending with a new saucer being attached to the old secondary hull, making it a fusion of new and old and giving it a sense of legacy.