History Main / OnceASeason

** The main character's partner recieving a DeadlyUpgrade before his proper NextTierPowerup. In the first two seasons it's Skullgreymon[[note]]in 02's case Agumon is a supporting character however[[/note]], Megidramon from ''Tamers'', and Shinegreymon Ruin Mode from ''Savers''. ''Frontier'' has a debatable case with Burninggreymon, which was initially out of Takuya's control before becoming a proper upgrade.

** Each season also has an [[FormulaBreakingEpisode "art episode"]], which experiments with the usual art style and/or storytelling, from doing a NoDialogueEpisode to a parody of ''[[Anime/TheAnimatrix The Second Renaissance]]''. Season 5 didn't have one, but the following season had two to make up for it.

Compare MandatoryLine, ADayInTheLimelight, OnceAnEpisode, MilestoneCelebration and any number of the holiday tropes such as ChristmasEpisode and HalloweenEpisode.

* ''Series/WhatWeDoInTheShadows'' gives the Baron a new look for each season in which he appears, for such reasons as Guillermo burning him or the Djinn giving him a makeover.

* ''WesternAnimation/Ninjago'': The mailman usually only appeared once per season as the show went on, which was lampshaded in [[Recap/NinjagoS8E76TheJadePrincess season eight]].

*** Season 8: [[Recap/DoctorWhoS34E3RobotOfSherwood "Robot of Sherwood"]]; [[Main/RobinHood Robin Hood]]. The Doctor is in disbelief about his very existence; he spends most of the episode trying to prove the folk hero is some sort of robot, hologram or alien clone. [[spoiler: He's real.]]

** After [[Series/{{Angel}} his departure]], Angel would show up for precisely two episodes a season in all but season 6 (when Buffy and Angel were on different networks, who [[ExecutiveMeddling didn't want the shows to be promoting each other.]]

** On a more ''meta'' level, since as early as Season 1, ''24'' has managed to predict an important item (usually a failure) of US foreign politics or military operations that actually takes place next year or a couple of years later '''in real life''': the first African-American President in Season 1 (way before its time); the US government [[AcceptableTargets blaming terrorist attacks on Middle-East countries]] to start a war for oil in Season 2; tortured or neglected agents defecting to the other side in Season 3; excessive demonization of arabs in the public media in Season 4; the US getting involved in the (mis)relationship between "mother Russia" and her annexed territories Season 5 (not to count revealing the President as the evil behind actually trying to start a war). Seasons 7 and 8 being the most recent ones it is not clear yet what ''24'' is going to end having predicted but it may be related to Sarah Palin as the first female President or American firms testing bioweapons in African countries (S7), or [[spoiler:the permanent damage that former Presidents have over the Office]] (S8).

** In the last episode of every season, one of the three human girls experiences a DisneyDeath. In S1, Sasha lets herself fall off the collapsing Toad Tower before Grime saves her. In S2, [[spoiler:Marcy was fatally stabbed through the back by Andrias' sword, before he eventually revived her to become the human host for [[MindHive The Core]].]] In S3, [[spoiler:Anne uses the power of all three Calamity Gems to destroy The Core for good, costing her own life in the process; she comes back to life when a celestial guardian [[CloningBlues makes a backup copy of her body]] and she refuses to take its place in the afterlife.]]

** Starting with Season 2's "Deal Me Out," Major Sidney Freedman appeared in one episode every season, save for Season 5 when he appeared twice.

* Before CerebusSyndrome plagued ''Series/{{MASH}}'' during its final seasons, in the beginning, the producers decided that once a season would have a DarkerAndEdgier episode; after a couple of seasons, they also decided to also have an episode or two a season that eliminated the laugh track altogether.
** As well, roughly once a season, there would be a "Letter to Home" episode, in which they would show brief snippets of life at the 4077th, with a FramingDevice of one of the main characters (usually Hawkeye in the earlier seasons) writing a letter to a loved one. (Although this has been played with several times. In one case, the FramingDevice was an official report Radar was filing, and in another it was a will that Hawkeye was writing while on a dangerous assignment. As well, another episode featured the entire cast writing letters to a class of schoolchildren.)

* ''{{Anime/Slayers}}'' had one [[WholesomeCrossdresser crossdressing]] episode every season, and it was always episode 17. This was due to the first series' IdiosyncraticEpisodeNaming. Episode 17 was the "Q" episode (thus making [[StealthPun a "queer" implication]]), and the tradition stuck until Evolution-R. ''That'' season did something else for the "Q" episode.

* One person dies per season in ''WesternAnimation/AvatarTheLastAirbender''. [[spoiler:From season one to season three, in order, that's: [[HotbloodedSideburns Commander Zhao]], [[WellIntentionedExtremist Jet]][[note]]Though it was often debated if he was actually killed before WordOfGod confirmed it.[[/note]], and [[TheSpeechless Combustion Man]].]] Also, one person gets burned by a fire-bender every season. In season one, [[Recap/AvatarTheLastAirbenderTheDeserter Aang burned Katara]]. In season 2, [[Recap/AvatarTheLastAirbenderTheChase Azula burned Iroh]]. And in season 3, [[Recap/AvatarTheLastAirbenderTheWesternAirTemple Zuko burned Toph]].