It's Christmastime again, which means its time for another Doctor Who Christmas Special. This year's Christmas Special, "Twice Upon a Time," is particularly meaningful for Doctor Who fans since it will be the final episode to star Peter Capaldi, who will regenerate from his own Twelfth Doctor into Jodie Whitaker's Thirteenth Doctor, and the final episode written by outgoing showrunner Steven Moffat, who will hand the series over to Chris Chibnall for its eleventh season. Moffat has been a part of Doctor Who since the series was relaunched in 2005. He's written for five different Doctors and six companions. Moffat began as a writer while Russell T. Davies was the showrunner on Doctor Who. Moffat made an impression by writing one standout episode after another until he became the obvious choice to replace Davies when a new showrunner was needed for the show's fifth season. Moffat transformed Doctor Who into something more like a science fiction fairy tale. Where Davies enjoyed referencing real-world popular culture, Moffat was always much more interested with Doctor Who's own mythology and explored its depths by asking questions of it that somehow hadn't been asked before in the series' 50-year history. Moffat also earned a reputation for heartbreak. His endings were often tragic or bittersweet, rarely delivering an entirely happy ever after. His Doctor Who could be fun, but often dealt with dark or heavy themes, ruminating on life and death and what why the Doctor would bother doing the things he does. To celebrate Moffat's time with the series, we're looking back through the years to choose his 10 best episodes of Doctor Who. These are all episodes written by Moffat himself dating all the way back to the first season of the new Doctor Who. There's one episode we couldn't consider for this list and that's "Twice Upon a Time." The Doctor Who Christmas Special airs Christmas Day at 9 p.m. ET on BBC America.

10. "Hell Bent" The season nine finale of Doctor Who gave companion Clara Oswald a powerful sendoff while allowed Moffat to but the more emotional side of the Twelfth Doctor on display. After the events of "Heaven Sent," the Doctor is more focused than ever and decides to actually attempt to cheat death for Clara, who perished in "Face the Raven." The Doctor literally stops time to pull Clara out of the moment of her death. What follows is a daring escape from Gallifrey, the hijacking of a TARDIS that is also an homage to the First Doctor, and a final showdown with Me. The ending perfectly subverts expectations of how this story would end, with the Doctor being the one whose memories are gone and Clara being in possession of her mind, as well as a brand new TARDIS. With Me by her side, Clara is ready for new adventures. prevnext

9. "The Girl in the Fireplace" "The Girl in the Fireplace" is an episode that puts the Doctor's heart on full display. The episode involved the Doctor finding a spaceship from the far future, but inside is a world that seems stuck in the 18th Century. The Doctor then meets the Madame de Pompadour, a young noble lady who is being watched at all times by clockwork robots. It turns out the robots are actually trying to repair the ship and that they're doing so with human body part. The Doctor manages to save everyone onboard and offers to take Madame de Pompadour with him. Unfortunately, time flows differently on either side of the lady's fireplace, leading to heartbreaking ending. prevnext

8. "The Empty Child"/"The Doctor Dances" Of Christopher Eccleston’s often overlooked single series playing the Ninth Doctor, Steven Moffat's two-parter “The Empty Child/The Doctor Dances” is the best story and the one where the new era of Doctor Who really begins to find its voice. The story has the Doctor and Rose Tyler (Billie Piper) traveling back to London during the blitz and discovering that a mysterious child is transmitting a strange disease throughout the city. These episodes showed the series could be campy, science fiction fun, unsettlingly creepy, and dig into tender, emotional territory in equal measure all in a single story. The episode also introduced Jack Barrowman as fan favorite adventurer Captain Jack Harness. prevnext

7. "Listen" "Listen" is an exceptional episode that cuts to the very roots of the entire Doctor Who mythology. The episode finds the Doctor investigating his idea that sentient beings are never truly alone, that there's some other creature who evolved to be perfectly hidden who is constantly with us even during our most private moments. After all, how would we know? The episode takes the Doctor and Clara to the childhood of Danny Pink first and then to the childhood of the Doctor himself. Clara ends up hiding under the Doctor's bed in a barn, the same barn the Doctor will return to as the War Doctor. She tells him that she's just a dream and then delivers a speech that would seem to inspire the Doctor to become the hero we know. "Listen" ends up being something nearly like an origin story for the Doctor, and a moment that will resonate throughout the entirety of his time as an adventurer, by cleverly inverting the usual Doctor-human relationship. prevnext

6. "Silence in the Library"/"Forest of the Dead" The Doctor Who Series 4 two-parter “Silence in the Library/Forest of the Dead” introduces River Song, the Doctor's wife, who would go on to become one of Moffat's favorite supporting guest characters and integral part of Doctor Who's mythology. It also lays out an incredible mystery: an empty library the size of a city, all of the people in it have disappeared, and for some reason we keep seeing flashes of a young girl spending time with her therapist. The story slowly reveals the answer, with David Tennant giving a fantastic performance as the Doctor deals with losing more and more innocent lives to the enemy in the shadows, eventually building up to one of those moments where the Doctor simply refuses to let anyone else die. There’s also a heartbreaking subplot for companion Donna Noble (Catherine Tate), who lives out a lifetime as a happy wife and mother before it all fades away. prevnext

5. "The Eleventh Hour" Steven Moffat's first episode as showrunner of Doctor Who was also Matt Smith's debut as the Eleventh Doctor and both made their marks immediately with the tightly-written season five opener "The Eleventh Hour." The first episode for a new Doctor is often awkward, as the new actor is still growing into what their version of the character should be, but Moffat provided Smith with an excellent, fast-paced episode to capture audience’s imaginations. The episode also introduces Karen Gillen as companion Amy Pond, “the girl who waited,” and begins the fairytale relationship between her and her “raggedy man.” prevnext

4. "World Enough and Time" Steven Moffat was in top form when he wrote the penultimate episode of Doctor Who Season 10, which is full of the kind of twists and references to Doctor Who mythology that fans have come to expect and anticipate from his work. Throughout the tenth season of Doctor Who, the Doctor was desperately trying to rehabilitate Missy. He had her trapped in a vault but let her out for her first adventure on a colony ship in space. Things go terribly wrong when companion Bill Pots is captured and brought ot the lower levels of the ship, where an entire city has sprung up in an are where time is moving at an accelerated pace. She spends years there with only one friend...and its that friend who betrays her and forces her to become a Mondasian Cyberman. That so-called friend eventually reveals himself to be the Master in one of the most tragic turns in Doctor Who history. If Steven Moffat has a talent, it's knowing how to hit Doctor Who fans where it hurts. prevnext

3. "The Day of the Doctor" (Photo: BBC) The 50th Anniversary Special, “The Day of the Doctor,” is a bit on the fanservice side, but when you're celebrating the 50th birthday of an institution of science fiction you earn some slack. The episode sees David Tennant return to reprise his role as the Tenth Doctor and team up with Matt Smith’s Eleventh Doctor to finally explore what exactly happened to the Doctor during the Time Wars. It’s unfortunate that Christopher Eccleston refused to return as the Ninth Doctor because his absence was felt, but John Hurt did a stellar job as the newly introduced War Doctor. Billie Piper also returned, though not as Rose, and classic Doctor Who star Tom Baker made a cameo appearance. We even got a first look at the Twelfth Doctor’s eyebrows. All in all, it was a sound celebration of the Doctor’s history. prevnext

2. "Heaven Sent" "Heaven Sent," the penultimate episode of Doctor Who Season Nine, is a near perfect episode of Doctor Who that puts all of Moffat's greatest strengths on display. In the episode, the Doctor finds himself trapped in a mysterious island castle prison. The first portion of the episode sees the Doctor exploring the island to try to piece together what has happened. It is a slow burn that pays off when the pieces ultimately fall into place. The Doctor is actually caught in some kind of time trap. His only way out is behind a thick diamond wall. This is where the Doctor shows what he's made of. He chips away at the diamond wall, punching with all of his might until he dies only to be resurrected and start the process all over again. The Doctor spends approximately 4.5 billion years repeating this cycle until he finally frees himself. The beautifully directed episode is one of the greatest testaments to the Doctor's strength of will that's ever appeared in the series. This use of mystery plotting to give the Doctor's indomitable spirit a chance to shine is Moffat at his best. prevnext