History WhatHappenedToTheMouse / WesternAnimation

* ''WesternAnimation/StevenUniverse'': "[[Recap/StevenUniverseS4E6LastOneOutOfBeachCity Last One Out of Beach City]]" has Pearl try out being wild and spontaneous for a night, going with Steven and Amethyst to a concert. She meets a human woman who looks like Rose, and manages to get her phone number (the episode only gives her first initial "S", but WordOfGod says they were calling her Sheena). It seemed like the two were going to hit it off and the Crewniverse even confirmed the Mystery Woman would return, but other than a background cameo in season 5, she was never seen again.

* ''WesternAnimation/StevenUniverse'': ''[[Recap/StevenUniverseS4E6LastOneOutOfBeachCity Last One Out of Beach City]]'' has Pearl try out being wild and spontaneous for a night, going with Steven and Amethyst to a concert. She meets a human woman who looks like Rose, and manages to get her phone number (the episode only gives her first initial "S", but WordOfGod says they were calling her Sheena). It seemed like the two were going to hit it off and the Crewniverse even confirmed the Mystery Woman would return, but other than a background cameo in season 5, she was never seen again.

* ''WesternAnimation/JurassicWorldCampCretaceous'': In season 2, the campers go through a whole episode and fight off a ''T. rex'' to send off an emergency beacon in hopes of being rescued. After they're forced to leave, the audience sees the beacon clearly displays "Message Received." As of season 4, not only has there been no follow up to this, but groups who should have knowledge of a message--[[spoiler: Mitch and Tiff in season 2, using stolen Jurassic World tech; Dr. Wu's team in season 3, actual Jurassic World employees coming to retrieve his research; Mantah Corp employees in season 4, who have been committing corporate espionage against Jurassic World]]--don't bring it up, even in context of "Wow, that wasn't some fluke!", While Season 5 confirms that Mantah Corp did indeed receive the beacon, there is no follow-up on why no one on the mainland (who the emergency beacon was presumably intended for) ever received and answered the beacon.
** Several species, variants of certain species or even individual dinosaurs that either did not appear in the previous Film/JurassicPark / Film/JurassicWorld movies and debut or returned after a long absence in the show but have yet to return post-Film/JurassicWorldFallenKingdom. Leaving it uncertain if they perished on Isla Nublar prior to or during Mount Sibo's eruption or if they were among the rescued dinosaurs that escaped Lockwood Manor.
*** Ouranosaurus, Which first appeared in season three in "Safe Harbor" and was last seen in a blink-and-you'll-miss-it cameo among a herd of stampeding dinosaurs in "Eye of the Storm".
*** Monolophosaurus, which first appeared in the third season in "Casa De Kenji" and was last seen when a pair were lured by Brooklyn in "Stay on Mission".
*** Ceratosaurus, which first appeared back in Film/JurassicParkIII and after a long absence returned in the "The Watering Hole" and would make subsequent appearances throughout the series until it was last seen on Nublar in the season 5 episode "Clean Break".
*** Bioluminescent Parasaurorolophus, a herd of them first appeared in the first season in "Welcome to Jurassic World" and after a various appearances where several of them were killed the Scorpius Rex, an individual was last seen in the season three in "Stay on Mission".
*** Chaos the Baryonyx, who first appeared alongside her siblings/pack-mates Grim and Limbo in the second season in "The Art of Chill" and subsequently menaced the main characters as a group on several occasions until [[spoiler: Grim was shot by a EvilPoacher and later Limo was stolen and relocated to another island where she seemingly died while fighting a Tyrannosaurus, with Chaos as the SoleSurvivor of her pack,]] making her last appearance in the fifth season in "Clean Break".
*** Tarbosaurus which has made its first and only appearance in the CYOA interactive episode "Hidden Adventure".

** The last you ever see of the Tree of Harmony's sentient form, an ethereal Twilight Sparkle, is in Uprooted when it explains how the actions of the Young Six have brought it back to life and made it stronger than ever due to their friendship. It plays no role in the series after that, is never mentioned again, and doesn't even appear during the BigDamnHeroes moment in the {{Series|Finale}} or DistantFinale.

** Several species, variants of certain species or even individual dinosaurs that either did not appear in the previous Film/Jurassic Park / Film/JurassicWorld movies and debut in or returned after a long absence in the show but have yet to return post-Film/JurassicWorldFallenKingdom. Leaving it uncertain if they perished on Isla Nublar prior to or during Mount Sibo’s eruption or if some or all of them were among the rescued dinosaurs that escaped Lockwood Manor.

*** Monolophosaurus, which first appeared in the third season in "Casa De Kenji" and later returned when a pair were lured by Brooklyn in "Stay on Mission".

*** Chaos the Baryonyx, who first appeared alongside her siblings/pack-mates Grim and Limbo in the second season in "The Art of Chill" and subsequently menaced the main characters as a group on several occasions until Grim was shot by a EvilPoacher and later Limo was stolen and relocated to another island where she seemingly died while fighting a Tyrannosaurus, with Chaos as the SoleSurvivor of her pack and making her last appearence in the fifth season in "Clean Break".

* ''WesternAnimation/JurassicWorldCampCretaceous'': In season 2, the campers go through a whole episode and fight off a ''T. rex'' to send off an emergency beacon in hopes of being rescued. After they're forced to leave, the audience sees the beacon clearly displays "Message Received." As of season 4, not only has there been no follow up to this, but groups who should have knowledge of a message--[[spoiler: Mitch and Tiff in season 2, using stolen Jurassic World tech; Dr. Wu's team in season 3, actual Jurassic World employees coming to retrieve his research; Mantah Corp employees in season 4, who have been committing corporate espionage against Jurassic World]]--don't bring it up, even in context of "Wow, that wasn't some fluke!"

** "Squid Baby": SpongeBob and Patrick come into the Krusty Krab zonked out after 72 straight hours of pampering the baby-morphed Squidward; after Patrick falls asleep on one of the tables, he is gone for the rest of the episode.

** "The Night Patty": Patrick just disappears from the episode after [=SpongeBob=] fills in for the night shift fry cook.

** And then there's Red X who was originally [[spoiler:Robin in disguise]], only for the costume to be stolen by an unknown thief. After his final appearance being in "Revved Up" he is never seen again (not even during the final battle in "Calling All Titans"). We never find out who he was behind the mask or how he got the Red X costume.

Despite last episode ending with Odalia planning to find a new business partner, she never shows up in this episode, so it's unknown what her reaction would be to finding out that selling out her family and all of witchkind to become royalty was All for Nothing.

** In "Night of the Living Pharmacists", Norm appears briefly at the beginning, and then leaves for the rest of the episode.

** The entire premise of "Mermaid Man and Barnacle Boy IV" is that [=SpongeBob=] accidentally shrinks everyone with Mermaid Man's belt. At the end when he shrinks the town (and himself) the belt is nowhere to be seen.

* In ''WesternAnimation/DesxtersLaboratory'', Mandark's sister Lalavava is never seen again after her only episode. Mandark becomes an only child afterwards.

* In ''WesternAnimation/{{Barnyard}}'', the story essentially revolves around Otis, his dad, and his pregnant wife Daisy; Daisy later gives birth at the end of the movie. Come the spinoff series, ''WesternAnimation/BackAtTheBarnyard'', and both Daisy and her son are demoted to non-speaking background characters in early episodes. They're eventually never seen again, instead replaced with Abby, who becomes Otis's girlfriend.

* In ''WesternAnimation/TeenTitans'', Kitten disappears after her encounter with Starfire in "Calling All Titans", despite the fact that Killer Moth and Fang both appear in the ClimacticBattleResurrection. Kitten does just seem to be your average SpoiledBrat, having a half-moth father and a boyfriend whose head was a giant spider aside; she probably doesn't have any real combat training.

** Speaking of "Revved Up", after the race for Robin's special suitcase, he opens it for his friends just before the end of the episode (the contents of the suitcase remain a mystery to the audience).

** With [[spoiler: Ratchet's]] return in Decepticon Island Season 2 finale and [[spoiler: Bulkhead's]] return in Sick as a Bot, it was originally unknown what happened to the rest of Team Prime. [[spoiler: Enemy of My Enemy makes mentioned that every Autobot has been blacklisted by the High Council, who turned out to be Decepticons in disguise.]]
** The most glaring one is perhaps is Knockout, who pulled a [[spoiler: HeelFaceTurn at the end of Predacons Rising.]]
** The most above example is the BigBad Megatron. Several Decepticons are implied to either have not been aware that [[spoiler: Megatron [[HeelFaceTurn disbanded the Decepticon faction]] and is in exiled or refuses to accept his decision]]. Soundwave also attempted to contact Megatron in Collateral Damage but failed. This leaves Megatron to not appear anywhere in the show.

** Speaking of "Revved Up", after the race for Robin's special suitcase, he opens it for his friends just before the end of the episode (the content's of the suitcase remain a mystery to the audience).

** The Conqueror, after being defeated by Norman, has been set free of his neverending cycle of fighting, and wishes to join humanity (though humans flee from him out of fear, though, which rather irritates him). He's never seen, heard of or mentioned again after that. Apparently, eight foot tall humanoid talking lions just wandering about is [[UnusuallyUninterestingSight no cause for attention]].

*** Googie is one of several new love interests introduced in the Superstars 10 films (Snulu for Boo Boo, Desert Flower for Huck, etc) which originally they had planned to make a whole other set of Superstars 10 films with some sequels to the previous batch. But near all those got pushed to the way side in the Turner boyout, turning most of the characters to forever be lost mice.

** Considering that the planet that the series takes place on is [[spoiler:70% water]], it wouldn't be surprising if a great many of them were [[spoiler:crushed in the great pressures of the deep]]. Not to mention it is heavily implied that the "quantum surge" in the Season 1 finale destroyed or damaged most of the pods. The ones that created Quickstrike and Silverbolt were heavily damaged causing the scanner to fuse two beast modes together for them. More telling, early in Season 2 Rhinox comes across a "blank" stasis pod. This means the Spark of the protoform inside has been extinguished, meaning it is dead, which can lead the audience to assume the remaining pods that were not destroyed upon impact suffered the same fate. Rhinox basically says that as far as they know, all of the pods are dead after the surge. Tigatron and Airazor were going to go explore to see if there were anymore, but he didn't sound hopeful. Tigatron and Airazor never found any, so we can assume they all died except for Silverbolt, Quickstrike and Rampage.