20. Robert Fortier and James Doohan in By Any other Name (TOS)
Scotty gets Tomar drunk so he can steal his psychokinetic control box. It's a great acting scene because we get to see an alien get drunk for the first time ever on TV!
19. Kate Mulgrew in Bride of Chaotica! (VOY)
Janeway has to take on a Flash Gordon-esque femme fatale to end a war between aliens and holograms. She's loving every minute of it!
18. Robert Picardo in Darkling (VOY)
The Doctor adds some personalities from ancient historical figures into his program and emerges as a Mr. Hyde of horrific proportions.
17. Michael Dorn in New Ground (TNG)
Worf is my all-time favorite character and he has far too many moments to post. In this episode, he learns he has a son, walks in after his mate has been murdered, and takes his revenge on the Klingon who not only murdered his mate, but wrongfully dishonored his family. Not since The Princess Bridge has revenge been served so well.
16. Jennifer Lien in Warlord (VOY)
Regularly boring character Kes is suddenly overtaken by a sadistic tyrant bent on immortality at any price. Everything from the way she walked to the way she talked was different from Kes. This episode proved not only that Jennifer Lien could act, but that she could do a great job!
15. Nana Visitor and Rene Auberjonois with honorable mentions to Terry Farrell and Armin Shimmerman in His Way (DS9)
The beautifully acted scene has Kira Nerys has realized that she loves Odo, and fans were rooting for this moment for years. The chemistry is electric, and the reactions (especially Quark's!) are priceless.
14. Dwight Schultz in Nth Degree (TNG)
In his first episode, Hollow Pursuits, Reginald Barclay was a very timid and meek crew member of the Enterprise who used the holodeck as a substitution for reality. In Nth Degree, he is possessed by an intelligent and friendly (although not known till the end) alien essence, which turns him into a suave, confident, uber-smart playboy. At the end of the episode, after the essence has left him, he still maintains a small amount of that confidence which makes him a stronger supporting character.
13. Jonathan Frakes in Frame of Mind (TNG)
Is Riker losing his mind? Jonathan Frakes keeps us guessing till the very end of this mind-tripping episode on whether or not what he is experiencing reality, or if something heinous is happening to him! (Unfortunately, this was the only clip I could find and it doesn't have his best moments, but it does have some great ones)
12. James Doohan in Relics (TNG)
Scotty may be drunk again, but this time his sense of awe and nostalgia hits you right in the heart as he reminisces about the good old days on his Enterprise.
11. Jeremy Kemp and Patrick Stewart in Family (TNG)
A fight with his estranged brother Robert causes Picard to realize why he went to visit him in the first place: his encounter with the Borg is something he has no more strength to hold back anymore. This episode that follows The Best of Both Worlds really shows us how Picard really feels about what happened.
10. Jeri Ryan in Body and Soul (VOY)
The Doctor was about to be erased, so Seven of Nine downloads his program into her body. He completely takes over her body, and Jeri takes on Robert Picardo's movements and speech patterns to show how he would react to her situations!
9. Avery Brooks in Far Beyond the Stars (DS9)
Brooks' character of Benny has met with so much racial prejudice that he can't hold back anymore on what he thinks. His monologue is one great piece of writing as well.
8. Roxann Dawson in Blood Fever (VOY)
This is what happens when a half-Klingon gets pon farr. Dawson does a great job of showing just how much of a struggle she's going through being out of control in her more extreme emotions (and you can definitely feel the heat). And speaking of pon far....
7. Leonard Nimoy in Amok Time (TOS)
....It also causes extreme uncontrollable actions. Spock thinks he has killed Captain Kirk and his reaction when he finds out Kirk is alive is truly an acting gem!
6. William Windon in The Doomsday Machine
Commodore Matt Decker is the only survivor and watched in agony as his crew was consumed by the Doomsday Weapon. His release here is one of the best of the guest appearances.
5. Nana Visitor and Harris Yulin in Duet (DS9)
Kira's hatred of Cardassians is put aside when she learns that the man she believes to be Gul Darhe'el is really an innocent man who is trying to get Cardassia to pay for their crimes against the Bajorans. The end result is also an extreme not quickly forgotten.
4. Patrick Stewart in Chain of Command part 2 (TNG)
Picard is being tortured by Cardassians for information. Stewart reportedly watches videos of torture victims to nail one of the finest performances of his career.
3. William Shatner in The City on the Edge of Forever (TOS)
You know that "Shatner-esque" form of acting that we so often see as a form of skewering actors? It may have been Shatner's form, but it doesn't apply here. This scene shows he actually is a good actor.
2. Tony Todd and Avery Brooks in The Visitor (DS9)
Tony Todd made several appearances in the spinoffs, but this scene here as a dying Jake Sisko reuniting with his dad after spending his lifetime trying to save Ben from the temporal loop he's caught in. One of the most touching moments ever caught in the universe.
1. Brent Spiner in Deja Q (TNG)
Q grants Data the one-time gift of a genuine laugh. Data goes from being himself to practically rolling on the floor with laughter and then back to his usual, emotionless self. It's a brilliant piece of acting and a scene that only Star Trek could make work!
