The X-Files is a supernatural science fiction horror thriller created by Chris Carter. Released in September 1993, the show lasted 11 seasons and 218 episodes. The first series was released from 1993 to 2002, and the second one was released from 2016 to 2018 under Fox. The show featured an ensemble cast that included David Duchovny, Gillian Anderson, Robert Patrick, and more.
Along with the series, two X-Files feature films were released in 1998 and 2008. The series follows two FBI agents, Fox Mulder, played by Duchovny, and Dana Scully, played by Anderson. Mulder is a supernaturalist and conspiracy theorist, whereas Scully is a medical doctor, initially skeptical about Mulder.
Throughout the series, Mulder and Scully become close friends after various conflicts about extraterrestrial life and realising what their government is hiding. The series features a story arc based on speculative science fiction along with weekly episodes that focus on a singular monster, alien, or mutant. The following list showcases some of the most rewatchable X-Files episodes.
Disclaimer: This list is based purely on the author's opinions.
Milagro, Squeeze, and five more episodes from the X-Files that are worth a rewatch
1) Pilot (season 1, episode 1)

The pilot was released on September 10, 1993, on the Fox network. Directed by Robert Mandel, it introduces the two main characters, Agent Mulder and Scully. The episode begins in the town of Oregon, where a teenager flees into the forest and is found dead. It is revealed that this is the fourth mysterious death in the town.
Throughout the 48-minute episode, the two special agents examine all the strange occurrences, including turbulence, bright flashes of light, disappearances in the forest, and exhumation of dead bodies. This is an iconic first episode as it sets the tone of the X-Files and is highly rewatchable.
2) Squeeze (season 1, episode 3)

The third episode of the series, Squeeze, was released on September 24, 1993, and was written by Glenn Morgan and James Wong. The main feature of this episode is Eugene Toomes, played by Doug Hutchinson. His core characteristic is the power of elongation, and being able to stretch and squeeze his body through narrow spaces.
Mulder and Scully, after going through painstaking efforts, find out that Toomes is a mutant who has been terrorising people for 90 years. Through the help of Frank Briggs, a retired detective, they find Toomes and begin to understand his life. Fans of X-Files will love this episode as it is the first one focused on a monster.
3) Paper Clip (season 3, episode 2)

The second episode from the third season premiered on September 29, 1995. Directed by Rob Bowman, the episode featured appearances by Sheila Larken, Nicholas Lea, and more. Paper Clip is the conclusion of a three-episode story involving the findings of Mulder and Scully regarding Operation Paperclip. They take down a nazi scientist obsessed with making alien-human hybrids.
The episode also progresses Mulder's arc with revelations about his father. This is another highly rewatchable episode from the X-Files.
4) Jose Chung's From Outer Space (season 3, episode 20)

Another episode directed by Rob Bowman and written by Darin Morgan, this episode was released on April 12, 1996. Apart from the protagonists, it features Charles Nelson Reilly in a guest role as the titular Jose Chung. This episode stands out because of its absurdity and satirical storytelling. Jose is an author who interviews Scully about an alien abduction.
As the episode progresses, it seems to make a mockery out of stereotypical tropes about aliens and tests the viewer based on their memory. Its unique storytelling makes it worth a rewatch while going through the X-Files directory.
5) Bad Blood (season 5, episode 12)

Written by Vince Gilligan and directed by Cliff Bole, Bad Blood aired on February 22, 1998. The guest star in this episode is Luke Wilson, who plays Sheriff Hartwell. The X-Files is popular for its witticism and unpredictable character depth, and this episode takes it up a notch as the agents narrate an incident. It showcases the contrast in their personalities and dynamics.
The episode also highlights their relationship with their superiors and offers an insight into their own. This episode is a must-watch for fans of Mulder and Scully.
6) Triangle (season 6, episode 3)

Released on November 22, 1998, Triangle was directed and written by Chris Carter. This episode gives a new perspective on the Bermuda Triangle, where Mulder finds himself on a ship. The time warp sends him back to World War II, making him disappear in the present. The most notable aspect of this episode is the use of continuous long shots and dual storytelling on the screen.
The X-Files usually features new guests on the show; however, this episode focuses on the adventures of Mulder, as Scully attempts to look for him in the present. The long shots, the Bermuda Triangle, and the differing storyline make it a compelling rewatch.
7) Milagro (season 6, episode 18)

Milagro is directed by Kim Manners and written by Chris Carter. It was released on April 18, 1999, and is focused on the two protagonists of the show, Mulder and Scully. The episode begins with the reveal of Scully's neighbor, who is shown to be a writer of fictional stories. As his behaviour begins to shift towards being obsessed with Scully, his stories also begin to convert into real murders.
In usual X-Files fashion, it delves deep into the nuances of reality and fiction, obsessive behaviour and the art of creation, making this another great rewatch.
Some more iconic episodes from the X-Files series are Clyde Bruckman's Final Repose, Post-Modern Prometheus, Quagmire, and Home.