The 4400: Just under half of the episodes were like this. Several episodes would focus on a specific person out of the forty-four hundred people who had disappeared and been returned (and, later on, people who had taken the Promicin shots handed out by Jordan Collier), what sort of supernatural power they had developed, and a problem they had created (either willingly or otherwise) that would be resolved by the end of the episode. As stated above, it could in this case perhaps be more accurately called something like 'Freak of the Week', as the people in focus weren't always deliberately antagonistic.
Agents of S.H.I.E.L.D.: The show starts off this way, though the Centipede organization and the mysterious Raina reoccur throughout various episodes.
Angel started by following this trope, but the format was discarded in favor of an arc-based one. Executive Meddling in season 5 brought it back full circle.
The Arrowverse tends to use this to differing degrees across its shows, in addition to all having a seasonal Story Arc and Big Bad:
Arrow itself has Corrupt Corporate Executive of the Week in Season 1, followed by a more generic Criminal of the Week in Season 2.
The Flash (2014) has a different metahuman criminal every episode, similar to the earlier example from Smallville mentioned below.
Supergirl (2015) has a different superpowered criminal or villain every week, though they're mostly aliens or alien-related in season 2.
The Aquabats! Super Show! gleefully indulges in this, and its monsters run from the fairly standard to the truly bizarre.
Babylon 5 had these from time to time, most often in the first two seasons, with Story Arc episodes mixed in and becoming more common as the show continued. By the third season, such episodes became very rare as the plot began to reach critical mass.
The series interspersed monster of the week episodes with Story Arc episodes, especially toward the beginning of the season. This became less common in later seasons.
Vampire Willow was this for two weeks.
Eyghon the Sleepwalker, although he becomes much more important in Angel & Faith.
Burn Notice episodes usually worked within a dual structure where Mike and his friends helped a Client of the Week fight a Loan Shark/Drug Dealer/Gang Member of the Week while also investigating the larger Myth Arc about Michael's burn notice. Mike almost always completely out-classed the villain of the week, so the larger arc was usually a chance to humble him and show him struggling with an equally matched opponent.
El Chapulín Colorado had most of its episode base on a Monster of the Week/Villain of the Week dynamics, although most monsters were a "Scooby-Doo" Hoax, so probably will be more accurate to say always Villain of the Week.
Charmed utilized this, although it became less prevalent in later seasons.
Chou Sei Shin Gransazer actually averts this trope for most of the series. The first 12 episodes has an alien agent put the Gransazers against each other. The next quarter of the show deals with a trio of recurring villains. Only the third quarter of the show has the heroes consistently deal with random monster attacks, which subsequently get replaced by another set of recurring villains in the final arc.
Criminal Minds has a new case almost every week (through at least Season 3) — usually dealing with the type of people you could call "monsters".
Dark Angel: The second season is a good example of this trope, with new transgenics popping up in several episodes who need to be either fought or helped, after Max released all of them from the burning Manticore facility in the season premiere.
Dark Shadows often had season-long arcs like this with one supernatural villain.
The "To Catch a Predator" segments of Dateline generally featured Pedophiles of the Week.
This show was originally supposed to be an edutainment program... until the Daleks showed up, whereupon it careened irreversibly into monster of the week territory.
Notably, the old series was made up of serials, usually three or four parts... making it more like monster of the month. Though, the new series follows this trope straight, while also including more Story Arcs.
They even lampshade this trope in "The Eleventh Hour", during Matt Smith's epic speech: "'cause you're not the first to have come here, oh, there have been so many!"
"Amy's Choice" parodies it by having the Doctor able to identify the species possessing the elderly and why they're on Earth without them even having to say anything, since it's All Just a Dream.
Farscape had monsters of the week interspersed with the Story Arc episodes throughout the series.
Forever. Although Adam is the primary villain of the series, it's still a cop procedural, with weekly cases and criminals.
Forever Knight: Nick Knight generally faces a new criminal every week in his job as a metropolitan police detective. Recurring villains include his vampire sire LaCroix.
Fringe starts out as primarily a monster of the week show, but later on they're either in service of or serve as a distraction to the Myth Arc.
The adult-oriented Toku GARO has monster of the week episodes spliced in with Story Arc episodes. On several occasions, the MOTW turns out to be relevant to the arc.
In every episode of the Girls x Heroine! shows, the main characters have to fight a human who has been brainwashed through touching a corrupted MacGuffin.
Grimm: The first half of the first series follows this to a tee. The second half of the series featured more character arcs and ongoing plotlines but it still largely stuck with one case every week, whether certain cases fed into a previous one or not.
In HarmonQuest, a part-animated series, part-improvisational comedy show where Dan Harmon invites comedians and actors to play Dungeons & Dragons in front of a live studio audience, the special guest players usually takes this role as their characters become the episode's villain of the week (in cases where the character doesn't die at the end, they just make an excuse to go their separate ways instead).
Haven revolves around the supernatural mystery disaster of the week. The town seems to attract people who are "troubled" and have supernatural abilities.
Heroes: This show is normally entirely serialized, but volume three would often put the arc in the background for a one-off evolved human. Examples include the man who could create wormholes and the Haitian's brother.
Highlander often had an evil Immortal of the week, due to the need to have a sword duel Once an Episode.
While Homicide: Life on the Street did have recurring villains, most episodes centered around the detectives tracking down a new criminal. Notably, many episodes followed multiple investigations, meaning they had multiple Villains of the Week.
Hunter: With the exception of a few double episodes, Rick Hunter and DeeDeeMcCall will always investigate one case a week involving a criminal who will be either locked up or shot dead by the end of the episode.
Kamen Rider, being a Tokusatsu franchise, has this as a staple. The following list includes notable implementations or subversions and aversions to this trope:
The first and second monster in the original Kamen Rider series are the Spider-Man and Bat Man respectively. note Not to be confused with the famous comic book heroes. The first monster to appear in more than one episode was the Cobra Man. Many of the newer Kamen Rider series reference all three by either basing the first monsters a Rider would face on these animals, or basing important antagonists on them.
The 51 Undead in Kamen Rider Blade are actually in conflict with one another to see which will be the dominant species on Earth (the human Undead was the winner of the last such competition, hence us). It can probably be assumed most of them are simply laying low and gathering their strength at the beginning of the series.
Multiple shows starting with Kamen Rider Den-O are a slight variation on this, as almost every episode is a two-parter (or more); therefore, almost every monster of the week actually lasts at least two weeks — and that's not counting the ones that were just slightly rebranded and reused, or those revived to serve as the Big Bad's army in the Grand Finale.
Kamen Rider Gaim, Kamen Rider Ex-Aid and Kamen Rider Build each introduce a small array of monsters at the start of the show, but transition away from monsters as the primary threat to focus on conflicts between multiple Riders with different philosophies or motivations. Only near the beginning of each show are single monsters treated like a genuine threat, with appearances afterward being more like Elite Mooks. Ex-Aid puts an extra twist on the formula by having there only be about ten to twelve monsters; they just have Resurrective Immortality. This ties into the series theme of comparing death in video games to death in real life.
Kamen Rider Drive establishes in its first episode that there are exactly 108 monsters, mooks included, which means that killing a mook is equally valuable to killing a named monster when it comes to making progress towards the series goal. Between the show, its movies, and all of the specials, it's possible to track exactly where all 108 are killed.
Kamen Rider Ghost eventually drops using individual Gamma as notable threats in favor of the Gammaizers, unique monsters with Resurrective Immortality. The Gamma costumes are recycled by Igor, who can use them as a dark mirror of Ghost's own Multiform Balance.
One distinguishing feature of Kamen Rider Zi-O is that, thanks to the show’s Time Travel gimmick, almost all of its weekly monsters are monstrous versions of the franchise’s previous Kamen Riders, starting with Build and working down from there.
Kamen Rider Zero-One has one set of monsters (androids hacked into killer robots) for the first third of the show, which are usurped by a second set (humanshacked into killer cyborgs) during the second act. The third act turns both types of monster into mass-produced mooks for the named antagonists.
Kamen Rider Saber gradually phases out the biweekly Mamono for a single Increasingly Lethal Enemy which has all of their individual powers combined, in addition to the usual slate of evil Riders.
Kamen Rider Geats has "Mooks of the Week" where the Riders would have to fight a different variant of Pawn Jyamato in each round of the Desire Grand Prix.
Kolchak: The Night Stalker could be considered the ultimate archetype. It was, in fact, even mockingly dismissed by some as "Kolchak's Monster of the Week" when its transfer from a pair of movies to a TV series ended up not quite panning out.
Legacies generally follows this format, as the main villain keeps sending monsters after MacGuffins in season 1 and after Landon in season 2.
Merlin: This was a big part of the first series, and the Big Bad only appeared in 4 of the 13 episodes. From Series 2 onwards the writers concentrated more on a singular villain (Morgause, Morgana and Agravaine, though occasionally a one-off monster will appear for a Filler episode.
In the first episode of Chōjinki Metalder, every monster from the show can be seen in the Big Bad's lair. There are four groups of monsters, each with its own general, and each has his or her own rank. Most are just in the background until it's their turn at being MOTW, but there are monsters who live to tell the tale and come back to fight another day multiple times, and some who rise to become major characters even if not "Victorious Saint" (general) rank.
Sekai Ninja Sen Jiraiya had a different World Ninja of the week, although quite a few survived their initial episode and went on to reappear, forming a Rogues Gallery of sorts. Not all of them are evil as well and some of them even become Jiraiya's allies.
Episodes of the RescuePolicetrilogy each feature a different "criminal of the week" who the Rescue Police have to stop, though uniquely for the franchise all of them are independent from each other, as the shows all lack a Big Bad or any sort of overarching threat.
Tokusou Robo Janperson doesn't have as many monsters, but they do have a "Cyborg of the Week" who fits the same mold, being a character that fights the heroes, gets defeated, and never seen again after their episode.
Every episode of Monster Squad had Count Dracula, Frank N. Stein and Bruce W. Wolf fight a different supervillain.
The format of Monster Warriors. Every episode Klaus Von Steinhauer (or, more rarely, someone else) creates a monster (intentionally or unintentionally) which attacks Capital City and the Monster Warriors have to stop it. The monsters are generally the sort of creature one would find a 1950s giant monster movie because Big Bad Klaus is an embittered film director from the 1950s who now has the means to bring his movie monsters to life.
Musica Piccolyno an NHK children's musical program takes this format. The main characters are 4 Musica doctors travelling a strange Steampunk dimension in their Cool Airship as each episode they try to help one of the Mechanical Lifeforms in that setting.
Painkiller Jane followed this formula, with the agency facing a different neuro every week.
Primeval: Just what will come through the Anomaly this week? Gorgonopsid? Mammoth? Velociraptor? Future predator? Knight in Shining Armor? The show also has a Story Arc that ran parallel, with the heroes battling human villains while still handling the monsters of the week, who filed both sides under "dinner".
Mighty Morphin' Power Rangers would take the monsters from Zyuranger, Dairanger, and Kakuranger and change them into Evil Space Aliens, with most of them being created by either Rita, Finster, or Lord Zedd. Some monsters, such as Madame Woe, Mondo the Magician, and the Face Stealer were not created by any of them, as they had already existed. (There were also MMPR-exclusive monsters, part of the "Zyu2" footage created by Toei exclusively for MMPR when it became clear the show was a runaway success.)
Power Rangers Megaforce first had Insectoids (aliens resembling different insects), followed by the Toxic Beasts (monsters born of pollution who joined forces with the Insectoids), and finally, the Robots Vrak created.
The Prisoner (1967) had the No. 2 of the week, who tried the scheme of the Week to attempt to break No. 6. (There were a couple of returning No. 2s with new schemes.)
Red Dwarf goes this way after about the third series. To their credit, the crew is pretty Genre Savvy about it, especially in Series 6. For example, Rimmer explains to one monster that everybody they'd met to that point has tried to kill them. It also swings the other direction in Series 7 & 8, having the storylines cover multiple episodes. (Although they are still self-contained.)
Seven Star Fighting God Guyferd: Each episode had Crown sending a different mutant monster to either defeat Guyferd or complete a part of one of their evil schemes.
The show has the "meteor freak" of the week, mutants created by Kryptonite. Season 6 also gave us the Phantom Zone escapees-of-the-week. As the series has progressed, it has much more of a Story Arc, but also keeps the Monster of the Week format.
It also had an interesting variation starting in Season 4: Hero of the Week. Every season would have about two or three episodes where a superhero or two from the comics would guest star, run amuck, get on Clark's bad side, then ultimately they'd make their peace and help each other out before leaving in a manner that some could interpret as a Poorly Disguised Pilot. The CW's second superhero show Arrow seemed to play with this method when it introduced Huntress: at first she seemed like she was going to be a hero of the week, then her second episode has her declare she'd rather practice revenge, not justice, then her third has her cross the Moral Event Horizon, turning her into a villain-of-the-week.
Space: 1999: One of the most common fan complaints about the second season was that it dropped the metaphysical and psychodrama aspects in favour of more monster-of-the-week action-oriented stories.
Spider-Man (Japan) has Professor Monster's Machine BEMs serve this purpose, with nearly every episode having a different monster assist the Iron Cross Army in their evil schemes until Spider-Man ends up soundly defeating them, frequently with the help of his Humongous Mecha Leopardon.
In SF author David Gerrold's book about writing the episode "The Trouble With Tribbles", he recounts seeing the first episode broadcast, which featured a creature that sucked all of the salt out of people's bodies, thereby killing them. He hoped Star Trek wasn't going to turn out to be a monster of the week show, which ironically for him, it did.
Supernatural usually has actual monsters, more so in the first two seasons. This is balanced against the Myth Arc villains, who tend to be demons, rogue angels, and, in Season 7, Leviathans. In the later episodes, where the Myth Arc dominates because of Villain Pedigree, the writers still bring in a monster of the week every once in a while for a breather.
Super Sentai has traditionally had these throughout their run.
Himitsu Sentai Gorenger has the Masked Monsters, the Black Cross Army's field agents known for their bizarre masks and deadly skills.
J.A.K.Q. Dengekitai has the Machine Robots, who were around for the early episodes until Shine was introduced in Episode 23. After that, they were replaced by the Invader Robots.
Choudenshi Bioman features an interesting variation of the formula. Instead of the villains sending monsters to fight the team on foot, they instead send the Beastnoids, a recurring Quirky Miniboss Squad of five monsters, to fight the Rangers human-sized and send separate giant creatures (and later giant robot creatures) to fight the Rangers giant-sized in mech battles.
Gosei Sentai Dairanger had the Gorma Monsters, a group of humans from an ancient tribe that were able to transform into more monstrous forms.
Ninja Sentai Kakuranger had the Yokai, who were released when Sasuke and Saizō wound up opening the gate that had them sealed.
The Jakanja in Ninpuu Sentai Hurricaneger have four monster divisions - the Puppet Ninja Corps, Alien Ninja Corps, Masked Ninja Corps and Phantom Beast Ninja Corps - each led by a different commander, who all take turns sending out one of their members to cause havoc. (They also had a corresponding growth method for each Corps.)
Tokusou Sentai Dekaranger had the Alienizers, intergalactic criminals that would target Earth for nefarious ends. Unlike previous and future series, rather than working directly for Agent Abrella, he would offer them weaponry, robotic foot soldiers, Heavy Industrial Machines and all assorted illegal items for conducting unlawful activities provide that they would willing to pay his exorbitant prices.
Mahou Sentai Magiranger has the Hades Beasts and Hades Beastmen. Due to a seal that was placed on the Infershia, they are not allowed to send in more than one monster.
Although there are four villain groups in GoGo Sentai Boukenger, the Jaryuu Clan and Dark Shadow are the only two who regularly make use of monsters of the week. The Questers followed something akin to a "Humongous Mecha of the Week" formula and Gajah rarely made use of henchmen that weren't his Mooks. Several episodes also saw the Boukengers going up against entirely independent monsters who embodied Precious artifacts.
Uchu Sentai Kyuranger had the Daikaan, basically "Evil Overlords of the Week" who each served as the overseer of one of the planets controlled by the Space Shognunate Jark Matter. After defeating enough of them, the Karo, the star system governors the Daikaan answer to, started picking fights with the Kyurangers as well.
Avataro Sentai Donbrothers features an unique twist: the Hitotsu-Ki are monstrous Oni forms taken on by humans with extreme desires in their hearts and are fought by both the heroes and villains with the difference that the Donbrothers seek to turn them back to their original human selves while the Noto simply destroy them, killing the host in the process, in order to stop them from disrupting the Noto Layer that keeps their world hidden from the human world.
Torchwood... At least, the first two series. After the successful switch to "mini-series focused on a single threat" of Children of Earth, RTD decided to drop the MOTW format altogether.
Tracker (2001) had a different alien fugitive each week. Sadly even Adrian Paul, who played Cole, felt that they got stuck in this formula and the show suffered because of it.
In the series, monsters of the week were produced by a chemical compound called "Mix Master" which, once released into the valley, randomly scrambled together the DNA of all living things except humans. This created monstrosities ranging from acid-shooting plants to giant shrimp.
And one of them was defeated by the resident monster, El Blanco.
The Ultra Series, especially the original series, was built around this trope (except for the occasional Multi-Part Episode, as well as any battles against a Big Bad). However, a large number of these weekly monsters end up becoming recurring opponents that face the Ultras multiple times if they become extreme popular with fans, creating a sort of Rogues Gallery in the process.
In a few series, the majority of MOTWs are recycled from previous shows due to the aforementioned Popularity Power. Ultraman Mebius, Ultraman Ginga, and Ultraman X are good examples, but Ultraman Max was the one that popularized the trend despite only eight monsters returning in that series. Additionally, some MOTWs might appear two or three times in a single series (eg: Baltan and Red King both appeared twice in Ultraman). Most fans are not bothered by this, since it means more opportunities to see their favorite monsters fight the Ultras.
When compared to other Toku franchises like Super Sentai, the MOTWs of the Ultra Series do not have any connection with each other and are treated much like natural disasters or animals-on-the-loose (ie: they do not serve the Big Bad), as popularized by the original Ultraman. This is averted in some series, like Ultraman Gaia and Ultraman Ace.
Obviously, most MOTWs in the franchise are kaiju or aliens that can turn giant-sized, since they're the only things big enough to fight an Ultra. However, Ultra Q and its tworemakes feature a much broader variety of MOTWs, with supernatural phenomena and human-sized creatures straight out of The X-Files. Only a few Ultraman shows have since featured these as the primary threat of an episode, notably Ultraseven and episode 13 of Ultraman Tiga.
The Ultra Series sometimes turns the trope on its head by having friendlyMOTWs. While there are many times where such creatures end up becoming corrupted by evil forces, there are also plenty of times where they aren't. Often in such situations, the humans and Ultras have to protect or assist the monster in some way instead of just killing it. Ultraman Cosmos is a golden example of this, as almost all the monsters in that series were Gentle Giants, Non-Malicious Monsters, or Benevolent Monsters.
In case the point about the franchise's MOTWs being as popular as the heroes hasn't been hammered in to you yet, there have been whole series entirely centered solely around the kaiju with some of them such as Gomora and Litra, taking up the role of the heroic forces.
Averted in Ultraman Nexus, where each monster forms its own story arc that can run anywhere between two to four episodes, and sometimes longer.
Ultraman Geed has an interesting take on this scenario, where a good chunk of its MOTWs are fusions of MOTWs from previous series.
Of course, the many Ultraman copycats that form the "Kyodai Hero" genre also use the formula, notably Zone Fighter and Spectreman. The former should get a particular shoutout for having Godzilla showing up a few times to help Zone battle the Terror-Beasts. Two of his enemies, King Ghidorah and Gigan, also appeared as MOTWs!
VR Troopers had all the guys from Chōjinki Metalder, but no clear ranking system; any time they got destroyed it could be hand waved that, since they were virtual creations to start, Grimlord could bring them all back whenever he wanted (as to explain why they kept appearing in the stock footage of his lair day after day). Since they also adapted Jikuu Senshi Spielban and later Space Sheriff Shaider, so there were plenty of MOTWs who made the traditional one-off appearances. Eventually, Grimlord gets fed up with their failures and once he gets an upgrade that means he doesn't need them anymore, he slaughters all of them but his favorites and replaces them with stronger minions who he has made each week.
Warehouse 13 revolves around the Artifact of the Week, which can range from purely a MacGuffin all the way up to an actual Monster.
The West Wing does this metaphorically, with political crisis of the week, caused by idiot politician of the week (in fact, many episodes are around one week long).
The Witcher, while Ciri and Yennefer's arcs are more narrative, Geralt's arc for the first six episodes is a case of this, appropriately enough for a monster hunter.
The X-Files: The show alternated weekly monsters and Myth Arc episodes. The X-Files is famous for not quite wrapping up a MotW and closing with a The End... Or Is It? ending. Unusually, while most fandoms consider MotWs to be filler, a large group of X-Files fans consider the weekly monster episodes to be superior to the Myth Arc episodes, especially in later seasons... mostly because the latter were made up as they went along.
