History LastEpisodeNewCharacter / WesternAnimation

** Cooper from the original series. Presumably didn't have a greater role than one guest appearance in [[WesternAnimation/Ben10AlienForce the sequel series]] because he was generally disliked by the fandom.

* ''Franchise/{{Transformers}}''
** The ''multitude'' of new characters appearing in the three-part series finale of ''WesternAnimation/TheTransformers''. Of course, it turns out that it was going to be the premiere of a fourth season, but reworked into a series finale when the plug was pulled on the show at the last second. Similarly, the Constructicons first appeared in the final episode of the first season, "Heavy Metal War", and the Throttlebots in the two-part finale of the third season, "The Return of Optimus Prime".
** In ''WesternAnimation/BeastWars'', Tigerhawk shows up in the episode before the two-part series finale. He doesn't make it to the sequel series, ''WesternAnimation/BeastMachines'', having died going toe-to-toe with a ''warship'', because Hasbro wasn't sure wether [[MerchandiseDriven to release his toy or not]]. He might not really count given his being a fusion of Tigatron and Airazor though.
** ''WesternAnimation/TransformersPrime'' has Darksteel and Skylynx, two Predacons created just before the finale.
* ''WesternAnimation/YoungJustice2010'' was ScrewedByTheNetwork and LeftHanging, which is why the series originally ended with the appearance of [[Characters/NewGodsDarkseid Darkseid]]. Averted with the revival of season 3, which places a heavier focus on Darkseid and [[ComicBook/NewGods The New Gods]].
* ''WesternAnimation/WolverineAndTheXMen2009'' suffered a similar fate, which is why the series ends with the appearance of Apocalypse.

* The final two episodes of ''WesternAnimation/TimothyGoesToSchool'' were all about a new cat-girl in Hilltop School named Juanita. While she did recur a bit in some of the picture books, this introduction was all that was seen of her on the television series, which was canceled after its second season.
* The final episode of ''WesternAnimation/TheWuzzles'' sees a new Wuzzle named Tycoon moving in and befriending the main characters. While the series didn't make it to a second season, Tycoon did live on in the toy line, getting his own plush toy and storybook.
* In the GrandFinale and HalloweenEpisode of ''WesternAnimation/TheGrimAdventuresOfBillyAndMandy'', ''Underfist: Halloween Bash'', we are introduced to the [[BigBad evil]] marshmallow bunny Bun-Bun. Given one of the title cards at the end, he might have made a return of some sort, [[WhatCouldHaveBeen had the special become a series like it was supposed to]].
* In the GrandFinale of ''WesternAnimation/RegularShow'', after eight seasons of flip-flopping between Margaret and CJ, the TimeCompressionMontage during the WhereAreTheyNowEpilogue has Mordecai meet a bat woman named Stef during one of his art shows. The two immediately hit it off, marry, and have children.
* In ''WesternAnimation/{{Daria}}'', Tom makes his first appearance in the finale of season three, and ends up becoming a prominent character through seasons four and five as he dates Jane, and later Daria herself.
* ''WesternAnimation/TheLegendOfKorra'' introduces Bumi in the final moments of book 1, although he was already mentioned earlier. Kuvira is also spotlighted near the end of book 3 before becoming the BigBad of book 4.

* The GrandFinale of ''WesternAnimation/AdventureTime'' features Shermy and Beth, adventurers from hundreds of years in the future (likely Finn and Jake's {{reincarnation}}s) who form the episode's FramingDevice by listening to BMO.
* The first season finale of ''WesternAnimation/HarveyStreetKids'' ends with the introduction of Audrey's older sister Zoe and her friends Maria and Stu. Later, the second season introduces the show's incarnation of ComicBook/RichieRich.
** The GrandFinale has [[spoiler: the Harvey Girls' parents. Audrey has a single mother, Dot has two fathers, and Lotta has her parents and grandmother]].
* The final episode of ''WesternAnimation/WordGirl'', "Rhyme and Reason", introduces a villainous duo named Rhyme and Reason and is about them breaking up and having to figure out how to get back together while Becky's SecretIdentity of [=WordGirl=] is discovered by her best friend Violet.

* The final episode of ''WesternAnimation/{{WITCH}}'' brings in Agent Riddle and Sylla as the only people that can detect the magical final battle in the middle of the city. Sylla later appears as a new computer instructor. This appearance was setting them up for the next arc, but the series was not picked up for another season.
* The GrandFinale of ''WesternAnimation/DuckTales2017'' introduces twin sisters June and May, with the third sister from the comics (April) suspiciously absent because she's actually ''[[CompositeCharacter Webby]]''.
* ''WesternAnimation/TheRocketeer'': Norman Sinclair only appears in the last episode of the series.
* ''WesternAnimation/TheVentureBrothers'' introduced Jonas Venture Jr. in the finale of Season 1, and Red Death in the finale of Season 6. While the former was PutOnABus after two seasons and didn't return to the forefront until ''All This and Gargantua-2'' [[spoiler:[[BackForTheDead (only to die at the end of it)]]]], Red Death by comparison plays a ''much'' bigger part in Season 7.
* ''WesternAnimation/TheOwlHouse''

** The WhereAreTheyNowEpilogue introduces [[spoiler:Hunter's new Palisman, a blue jay named Waffle, who he carved after Flapjack's death in "Thanks to Them".]]

* ''WesternAnimation/YoungJustice'' was ScrewedByTheNetwork and LeftHanging, which is why the series originally ended with the appearance of [[Characters/NewGodsDarkseid Darkseid]]. Averted with the revival of season 3, which places a heavier focus on Darkseid and [[ComicBook/NewGods The New Gods]].

* ''WesternAnimation/YoungJustice'' was ScrewedByTheNetwork and LeftHanging, which is why the series originally ended with the appearance of ComicBook/{{Darkseid}}. Averted with the revival of season 3, which places a heavier focus on Darkseid and [[ComicBook/NewGods The New Gods]].

** The final episodes of ''Alien Force'' and ''WesternAnimation/Ben10UltimateAlien'' introduced [[EvolutionPowerup Ultimate Swampfire and Ultimate Way Big]]. ''Ultimate Alien'' plays this straight, as Ben receives a new Omnitrix at the end of the episode that (According to WordOfGod) does not possess the evolution function, meaning Ultimate Way Big will never be seen again.

** Since "Secret of the Omnitrix" is technically the real GrandFinale of the first series, Azmuth also qualifies.

** The GrandFinale has [[spoiler: the Harvey Girls' parents. Audrey has a single mother, Dot has two fathers, and Lotta has her parents and grandmother.]]

** In ''WesternAnimation/BeastWars'':, Tigerhawk shows up in the episode before the two-part series finale. He doesn't make it to the sequel series, ''WesternAnimation/BeastMachines'', having died going toe-to-toe with a ''warship'', because Hasbro wasn't sure wether [[MerchandiseDriven to release his toy or not]]. He might not really count given his being a fusion of Tigatron and Airazor though.

** In ''WesternAnimation/BeastWars'':, Tigerhawk shows up in the episode before the two-part series finale. He doesn't make it to the sequel series, ''WesternAnimation/BeastMachines'', having died going toe-to-toe with a ''warship''. He might not really count given his being a fusion of Tigatron and Airrazor though.

* In ''WesternAnimation/BeastWars'':, Tigerhawk shows up in the episode before the two-part series finale. He doesn't make it to the sequel series, ''WesternAnimation/BeastMachines'', having died going toe-to-toe with a ''warship''. He might not really count given his being a fusion of Tigatron and Airrazor though.
* The ''multitude'' of new characters appearing in the three-part series finale of ''WesternAnimation/TheTransformers''. Of course, it turns out that it was going to be the premiere of a fourth season, but reworked into a series finale when the plug was pulled on the show at the last second. Similarly, the Constructicons first appeared in the final episode of the first season, "Heavy Metal War", and the Throttlebots in the two-part finale of the third season, "The Return of Optimus Prime".
* ''WesternAnimation/TransformersPrime'' has Darksteel and Skylynx, two Predacons created just before the finale.

* The GrandFinale of ''WesternAnimation/KimPossible'' has Warhok, a DarthVaderClone and the greatest threat Kim and Ron ever faced.

* The GrandFinale of ''WesternAnimation/AdventureTime'' features Shermy and Beth, adventures from hundreds of years in the future (likely Finn and Jake's {{reincarnation}}s) who form the episode's FramingDevice by listening to BMO.

** Season 2 ends with the introduction of Ana, a well-known publicist nicknamed "The Oscar Whisperer" due to her clients almost always winning Oscars. She becomes a major character during season 3 as she helps Bojack get his awards.
** Season 3 ends with the introduction of the WalkingSpoiler that is Bojack's supposed illegitimate daughter, Hollyhock[[note]]Who turns out to actually be his half-sister in the following season.[[/note]].

* ''WesternAnimation/YoungJustice'' was ScrewedByTheNetwork and LeftHanging, which is why the series originally ended with the appearance of ComicBook/{{Darkseid}}. Averted with the revival of season three, which places a heavier focus on Darkseid and [[ComicBook/NewGods The New Gods]].
* ''WesternAnimation/WolverineAndTheXMen2009'' suffered a similar fate, which is why the series ends with the appearance of [[spoiler: Apocalypse]].