FX's horror anthology American Horror Story has made for some of the freakiest TV of the past few decades, but few episodes can rival the season finale of the fourth season. "Curtain Call" certainly lived up to its name, bringing the story of a circus show to a shocking and bloody end, which is saying something for a show that prides itself on shocks and scares. It's not afraid to take some interesting turns, and the final scenes brings the journey to a poignant finale.

The Buffy the Vampire Slayer spinoff Angel went out on a high note in its fifth season, and "A Hole in the World" is one of the most brutally heartbreaking episodes the show ever put to screen. It finds Wesley and Fred finally coming together after seasons of teases and tension, only for Fred to die in his arms after being infected by an ancient god. Her death is powerful and painful, and the fact that Angel would do something so game-changing in a 'regular' episode made it all the more shocking.

The CW rolled the dice on Arrow in 2012, and little could the network have known it would go on to spawn its own DC universe that would make up the brunt of the network’s schedule just a few years later. But, it all started here. The network was looking to differentiate the show from the slightly sillier slant of Smallville just a few years before, and basically turned Arrow into a small screen Batman Begins — and it worked masterfully. The pilot set the tone for a grounded superhero series that took the material seriously, and it helped pave the way for the superhero TV renaissance we’re currently enjoying from both DC and Marvel.

Thanks to its anthology format, Black Mirror has the freedom to tackle heady topics on an episode-by-episode basis. This take on grief and loss, tinged with a bit of sci-fi creepiness, is easily one of the show’s best episodes. Starring Hayley Atwell and Domhnall Gleeson, the story follows a woman who loses the love of her life, only to realize she's pregnant with his child. Unable to process the grief, she turns to an online service that aims to fill that void with an AI construct based on the deceased. Atwell plays every stage of grief perfectly as she climbs deeper down this ever-creepier rabbit role.

Joss Whedon's Buffy the Vampire Slayer is a seminal work of pop culture, buoyed by more than a few quips and vampire fights on a weekly basis. But "The Body" had virtually none of that. The episode focused on the death of Buffy's mother due to natural causes and follows the immediate aftermath of her passing. Whedon perfectly captured the confusion and grief that follows the death of a loved one in a much more naturalistic style than usual. It's visceral, brutal and one of the most raw hours of television ever conceived.

Not many shows could pull off an episode that features virtually no dialogue, but Buffy isn't most shows. "Hush" was one of the first times creator Joss Whedon really pushed the boundaries for the way he could tell stories on television, crafting a terrifying tale of gentlemanly monsters who steal the town's voices. It's littered with jokes tailor-made for the setup but is still easily one of the show's creepiest and finest episodes. Decades later, few shows have attempted something so weirdly ambitious.

HBO's acclaimed and short-lived dark fantasy series from the early 2000s sits relatively high on a whole lot of "Best Of" lists, and for good reason. The show was set in the Dust Bowl during the Great Depression and blended an ambitious story of faith and religion that asked heady questions about destiny. The pilot, "Milfay," had some heavy lifting to establish this world but did an excellent job of making it not just believable but compelling. It's the story of a man who leaves his troubled life behind to join a traveling circus, but there’s so much more bubbling under the surface.

If you've never seen an episode of Doctor Who — and know nothing of the show's decades of lore — you can still pick up "Blink" as a stand-alone vignette and walk away extremely satisfied. It's a story that puts the Doctor in the background and focuses on a young woman who accidentally stumbles into his weird, dangerous world. It’s the perfect example of a stand-alone episode, and the fact that they pulled it off in a show as complicated as Doctor Who is all the more impressive. It also gets bonus points for introducing the terrifying Weeping Angles to the world.

Farscape is one of the best space operas ever conceived, and a big part of what made it so beloved is the fact that it wasn't afraid to get a little weird. Case in point: "Revenging Angel." The brunt of the episode took place in a Roadrunner-esque animated form via a hallucination in Crichton's head. The show had always been ambitious, but "Revenging Angel" showed that literally nothing was off the table. It pushed the limits of the types of stories you could tell in a sci-fi show and had a heck of a lot of fun while doing it.

For such a short run, Joss Whedon's sci-fi western Firefly sure managed to do a whole lot of things before getting the axe. The show’s eighth episode, "Out of Gas," takes a non-linear approach to its story of the ship being critically damaged and the crew desperate to survive. In addition to the A-story of the breakdown, "Out of Gas" also digs into how the crew came together in the first place and touches on the events leading up to the ship's damage. It has great character moments and organically fills in the crew's backstory. Whedon has called the episode one of his favorite hours of television on any show, and it's easy to see why.

Fringe is one of the best modern-day sci-fi shows and prided itself on a complicated mythology featuring everything from myriad evil scientists to an alternate reality lovingly nicknamed 'Over There.' But "White Tulip" ties that serialized storytelling into a stand-alone episode, which uses time travel to perfectly wrap itself up in a bow. It follows a scientist who turns his body into a time machine in an effort to go back and save his fiancee, making for a stunning testament to the power of love and forgiveness.

This Emmy award-winning installment in the acclaimed sci-fi animated series is one of the best, serving as a time-bending and hilarious half-hour. The episode ties back into real-life history, revealing that Fry, Leela and the gang are actually to blame for the famed Roswell UFO crash in the 1940s after accidentally being sent back in time by a supernova. It tackles time travel and causality in very clever ways and even takes a few dark turns (turns out Fry is his own grandpa) along the way.

Game of Thrones is a show that's never been afraid to kill off its characters, but "The Red Wedding" took it to a whole new level ... then just kept slashing a few more throats for good measure. Sure, it was positively shocking to see a room full of people butchered, but "The Red Wedding" also killed off nearly one-third of the show's central cast in one fell swoop. It's the epitome of no character being safe, and fans are still talking about it years later.

This Danish miniseries from Lars von Trier inspired Stephen King’s Kingdom Hospital miniseries, but the original series is arguably a whole lot better than King’s adaptation. “The Unheavenly Host” served as the series pilot, introducing viewers to a mysterious hospital where doctors and patients begin to experience strange phenomena. It was smart, weird, small and some fantastic genre work from von Trier. Which, if you need more proof: just think of how many shows are good enough to actually inspire Stephen King to adapt it, right?

Lost was a cultural phenomenon in the mid-2000s, and "The Constant" was one of the most ambitious and well-executed episodes in the show's entire run. Framed around Desmond’s uncontrolled jumps to the past, the story takes a philosophical approach to time travel, setting up he and Penny’s relationship as his “constant,” the one thing that tethers him to reality and keeps him from going mad. It's Lost at its best, and a reminder that — no matter what you think of the series finale — this show made for some heartbreaking and clever science fiction along the way.

The X-Files-adjacent series Millennium might not have made as much staying power as the flagship series, but it still made for some fantastic television during its three-season run. It might've been a dark-fantasy, conspiracy crime thriller, but in "Somehow, Satan Got Behind Me," the story takes a break to focus on smaller vignettes as a few demons meet up at a donut shop to swap stories. It helped push the envelope for the types of stories that can be told in a sci-fi show and made the world of Millennium fell all the more organic.

There are many reasons why Bryan Fuller is an acclaimed television creator — and "Pie-lette" is a very big one. The series premiere for his short-lived cult hit series Pushing Daisies is a master class for how to take a quirky premise and present it perfectly, complete with poignancy and a whole lot of humor. With the story of a pie maker who can bring people back to life with a touch, Fuller found a way to tell a story unlike pretty much anything else on television, making "Pie-lette" is one of the most ingenious and masterful TV pilots of the modern era.

Stargate SG-1 is one of the longest-running sci-fi franchises in history and was the type of "meat and potatoes"” science fiction that served as a throwback to Star Trek: The Original Series. But it could still pull off a nice surprise on occasion. "Window of Opportunity" found O’Neill and Teal'c trapped in a time loop and perfectly captured the humor and frustration in repeating the same day over and over again. It's one of the funniest episodes in the series' run and put a fresh spin on what could've easily been a well-worn trope.

The Borg easily became one of the most compelling Trek baddies in the Next Generation era, but this episode is the one that actually used them as a way to ask some tough questions about identity and the way to treat your enemies. The story focuses on an adolescent Borg found by the Enterprise crew, and shows there’s a whole lot more to these things than their "Resistance is futile" catchphrase. It was an opportunity for Trek to push the boundaries into a rare grey area with tough ethical questions, and was handled masterfully.

The CW's Supernatural was originally conceived with a five-season story arc, and the fifth season finale "Swan Song" brought the series perfectly to a close. Sure, the series would go on to run for several more years (and is still going strong), but it doesn’t change the fact that "Swan Song" is one of the best series finales ever. Dean and Sam spent the entire series trying to catch the Yellow-Eyed Demon that killed their mother and finally come face to face with him as the apocalypse looms. The episode wrapped up five seasons of story perfectly.

There's probably no such thing as a 'typical' episode of Twin Peaks, but even for this bizarre and dreamlike show, "Part 8" felt like a bolt from the blue. It's essentially a 55-minute David Lynch experimental film, beginning with a horrific confrontation and then transitioning into nightmarish black-and-white visions of worlds and strange machines we'd never seen before. "Part 8" is about more than being weird, though. It feels like Lynch taking every trick he's ever learned from decades of filmmaking and weaving it all into an astounding masterwork. You'll never see a purer statement of unfettered imaginative.

The Walking Dead television show has taken the character of Carol in a very different direction from the comics and that was never more obvious than in "The Grove." The episode is a tour de force for star Melissa McBride, whose character enjoys a brief reprieve at an idyllic house she and her fellow survivors stumble upon. The episode sees the story of Lizzie — an unstable young girl unable to adjust to the dead coming back to life —come to a head as she kills her little sister. With no mental health options in the post-apocalypse, Carol makes the decision to kill Lizzie herself, since she can't be trusted not to kill anyone else. It's a brutal glimpse into how the end of the world has affected the survivors and positively gut-wrenching. Yeah, just look at the flowers.

Peak X-Files, this episode found the show doing what it did best: putting a fresh spin on its trademark "Monster of the Week" stories. In this one, the story focused on a man with the ability to foresee how people will die as he works with Mulder and Scully to unravel a series of mysterious murders. The episode stands out to this day for how well it perfectly balances an extremely dark story with splashes of humor. It's a textbook example of how to make the heavy not feel so heavy and the type of episode you can pick up with little context and still be blown away.

Sure, The X-Files was never afraid to go a little dark, but "Home" pushed the boundaries considerably. The episode focused on a disturbing case of a family with a long history of incest and was the first episode of the series to ever carry a viewer discretion warning for disturbing content. In addition to standing out as one of the show's best "Monster of the Week" stories when the program was in its prime, it also pushed the limit for what a mainstream show could get away with on network television.

These were all of OUR choices. But we're curious which of single episodes of sci-fi and fantasy television from the last 25 years you'd put on YOUR list? Let us know in the comments! And be sure to check out our complete 25 Greatest lists here.