This is an Ending Trope, so beware of unmarked spoilers!
Times where the final episode of a season or series introduces a new character in Western Animation.
- The Grand Finale of Adventure Time features Shermy and Beth, adventurers from hundreds of years in the future (likely Finn and Jake's reincarnations) who form the episode's Framing Device by listening to BMO.
- Batman: The Brave and the Bold's finale features Ambush Bug as the guest hero, despite him never having appeared in the show before.
- The last episode of Beetlejuice, "Not so Peaceful Pines", introduces the Mayor of Peaceful Pines, who makes the mistake of raising Beetlejuice's ire by declining to pay him a fee for getting rid of the town's noisy partygoers like he promised.
- Ben 10:
- Cooper from the original series. He didn't have a greater role than one guest appearance in the sequel series, presumably because he was generally disliked by the fandom.
- Since Secret of the Omnitrix is technically the real Grand Finale of the first series, Azmuth also qualifies.
- The final episodes of Alien Force and Ben 10: Ultimate Alien introduced Ultimate Swampfire and Ultimate Way Big respectively. Ultimate Alien plays this straight, as Ben receives a new Omnitrix at the end of the episode that (According to Word of God) does not possess the evolution function, meaning Ultimate Way Big will never be seen again.
- BoJack Horseman:
- Season 1 ends with BoJack doing a screen test for the Secretariat biopic with director Kelsey Jannings present. Season 2 involves the making of that biopic.
- 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 Walking Spoiler that is BoJack's supposed illegitimate daughter, Hollyhocknote .
- The final episode of Chowder gives us Chowder's apprentice, Scraps.
- In the final episode of Cro, a new human character was introduced named Sooli. After helping to tame a wild horse, Cro accepted her into the tribe.
- In 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.
- Averted in the finale of the Nickelodeon run of Doug. While the main character spends most of the episode trying to finally see what his principal, Mr. Butsavage, looks like, by the end of the episode, he barely misses seeing the principal give a speech, but stops worrying about it and finally starts celebrating the fact that he's graduating.
- The Grand Finale of DuckTales (2017) introduces twin sisters June and May, with the third sister from the comics (April) suspiciously absent because she's actually Webby.
- In Ed, Edd n Eddy, Eddy's brother shows up in the climax of Ed, Edd n Eddy's Big Picture Show. Up until then, he was only mentioned by other characters. This is even more notable considering he's the only new character introduced in the entire show after the main cast was established.
- In the Grand Finale and Halloween Episode of The Grim Adventures of Billy & Mandy, Underfist: Halloween Bash, we are introduced to the evil marshmallow bunny Bun-Bun. Given one of the title cards at the end, he might have made a return of some sort, had the special become a series like it was supposed to.
- The first season finale of Harvey Street Kids 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 Richie Rich.
- The Grand Finale has the Harvey Girls' parents. Audrey has a single mother, Dot has two fathers, and Lotta has her parents and grandmother.
- Invader Zim did this as well introducing Zim's new sidekick Minimoose in the final episode "The Most Horrible X-mas Ever". In a unique spin on this trope, this wasn't actually supposed to be the final episode of the show nor Minimoose's first appearance. An episode called "Nubs of Doom", which would've introduced Minimoose being made by Zim to replace Gir as a sidekick, was in development. Unfortunately, due to the fact that the show was canceled before it could even finish its second season, Minimoose's debut episode ended up having to remain unfinished with the Christmas special airing as the finale. Though considering the type of show this is, Zim suddenly having a tiny, floating moose as a second sidekick out of nowhere is par for the course.
- The Grand Finale of Kim Possible has Warhok, the greatest threat Kim and Ron ever faced.
- The third-to-last and second-to-last episodes of King Arthur & the Knights of Justice introduce warriors outside of the Knights of Justice who (have the potential to) defend Camelot. One of them even appears to be a fictionalized version of Clovis I, more or less the first king of France and a contemporary of the historical Arthur. Their introductions seem to be meant as counterweight against the Purple Horde on the evil side, but without a third season, their additions led to nothing.
- The Legend of Korra 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 Big Bad of book 4.
- The Grand Finale of My Little Pony: Friendship Is Magic introduces Luster Dawn, the student of Twilight Sparkle. Luster is used as the Framing Device for a Whole Episode Flashback explaining what happened at Twilight's coronation several years prior, as well as what happened to each of the show's main characters.
- The Owl House:
- The season 1 finale two-parter introduced the Golden Guard, Belos's right hand man (though his name wasn't given until the first episode of season 2), who was given the task of keeping an eye on the Owl House at the end of "Young Blood, Old Souls". He became a recurring villain in season 2, before defecting from the Emperor's Coven in "Hollow Mind" and pulling a proper Heel–Face Turn in "Labyrinth Runners".
- The "Where Are They Now?" Epilogue introduces Hunter's new Palisman, a blue jay named Waffle, who he carved after Flapjack's death in "Thanks to Them".
- In the Grand Finale of Regular Show, after eight seasons of flip-flopping between Margaret and CJ, the Time-Compression Montage during the "Where Are They Now?" Epilogue has Mordecai meet a bat woman named Stef during one of his art shows. The two immediately hit it off, marry, and have children.
- The Rocketeer: Norman Sinclair only appears in the last episode of the series.
- The final two episodes of Timothy Goes to School 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.
- Transformers:
- The multitude of new characters appearing in the three-part series finale of The Transformers. 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 Beast Wars, Tigerhawk shows up in the episode before the two-part series finale. He doesn't make it to the sequel series, Beast Machines, having died going toe-to-toe with a warship, because Hasbro wasn't sure wether to release his toy or not. He might not really count given his being a fusion of Tigatron and Airazor though.
- Transformers: Prime has Darksteel and Skylynx, two Predacons created just before the finale.
- The Venture Brothers introduced Jonas Venture Jr. in the finale of Season 1, and Red Death in the finale of Season 6. While the former was Put on a Bus after two seasons and didn't return to the forefront until All This and Gargantua-2 (only to die at the end of it), Red Death by comparison plays a much bigger part in Season 7.
- A much more straightforward use of this trope occurs in the actual series finale, Radiant is the Blood of the Baboon Heart, which introduces Big Bad Mantilla, though while technically a new character she is intricately connected to a number of other characters that are integral to the series, as well as a few others that have been mentioned in passing.
- The final episode of W.I.T.C.H. 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.
- Wolverine and the X-Men (2009) suffered a similar fate, which is why the series ends with the appearance of Apocalypse.
- The final episode of 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 Secret Identity of WordGirl is discovered by her best friend Violet.
- The final episode of The Wuzzles 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.
- Young Justice (2010) was Screwed by the Network and Left Hanging, which is why the series originally ended with the appearance of Darkseid. Averted with the revival of season 3, which places a heavier focus on Darkseid and The New Gods.
- My Adventures with Superman: Season One last episode "Hearts of the Fathers" ends with the introduction of Brainiac and a "Kryptonian Warrior" who will make the Earth kneel.
