Peter accidentally sets fire to the pediatric wing of a hospital while trying to impress his boss in order to get a promotion. Later, his boss puts his name down for consideration for an executive position. Later still, after Peter has graduated from the third grade in order to qualify for the position, his boss points out that there is no way he's getting the job because he set fire to a hospital, killing 19 children. She doesn't explain why she considered him for the position in the first place. The problem with Family Guy is that sometimes it's hard to tell whether it's a plot hole or part of the joke.
Gargoyles had one in the final episode of the third season. Broadway automatically knew that Angela and Bronx were in jail despite the fact that he had not yet been told about it, and otherwise had no way of knowing about it happening. A possible explanation is that he found out about it offscreen.
In City of Stone, Demona enters castle Wyvern through a secret passage and muses to herself that Xanatos doesn't know all its secrets. Somehow, Xanatos (and Owen), the guy who dismantled the castle AND rebuilt it in NY failed to notice this. Even if he subcontracted the whole thing to a firm, as a company executive, he must have seen the castle's blueprints more than once.
The Turtles and April meet the Neutrinos in the Season 1 episode "Hot Rodding Teenagers from Dimension X". In the follow-up Season 2 episode, "Teenagers from Dimension X", the Neutrinos are already acquainted with the Turtles, but are unfamiliar with April despite the fact that she was with the Turtles in the previous episode.
A truly baffling one happens in the Vacation in the Europe side season. In the first episode, Shredder and the Turtles run into each other in France, and fight on top of the Eiffel Tower. In the next episode, the Turtles are still in France, and not only do they talk about going to see the Eiffel Tower, Shredder is shocked when he learns they're in France. It almost seems like two season-opening episodes were made separately.
In the Kim Possible episode "Mind Games", Dr. Drakken swaps bodies with an army official in order to steal a superweapon. Kim and Ron rescue the captured army official, but all three are later captured again - Kim and Ron are tied to a post while the army official is hauled away by Drakken's guards. Later, Drakken decides to kill Kim and Ron with his base's auto-destruct. Not only does Drakken not just shoot them, they are rescued by the army official, who was apparently left in the same room with Kim and Ron without being tied up or anything! Also, he isn't visible in an earlier wide-angle shot of the room.
When we last see the Trix in Season 2, they are stuck in the Realix realm (in the Nickelodeon-produced episode, they were sent back to Lightrock Monastery), yet at the beginning of Season 3 they have somehow been arrested and dropped off in the Omega dimension.
Season 6 gives us a huge plot hole when they finally have the pixies return. It's not their return that's the plot hole. It's that two of them have been replaced with pixies from the spin-off with no explanation given whatsoever. The show treats it as if they'd always been bonded to Musa and Tecna, as if Tune and Digit never existed. Needless to say, many fans were not happy.
A really jarring one in Season 8: In the earlier seasons, it was established that the Trix are sisters who descended from the three Ancient Witches. However, in this season, suddenly they aren't sisters anymore; instead, Icy now has a different sister named Sapphire. Also, apparently she's now the princess of a planet named Dyamond. None of this was ever alluded to in the previous seasons and in fact contradicts not just those seasons, but also the first two movies. It could perhaps be argued that the Trix did in fact still descend from the Ancient Witches and that they're more akin to distant cousins, and are instead "sisters by choice", but this still contradicts statements made by Iginio Straffi years ago that the Trix are biological sisters and triplets.
Galtar and the Golden Lance: The eponymous weapon can only be used by Galtar (the show's continuity is pretty loose, but this has been the rule from Day 1), because he's the champion of all things Good...until someone breaks the rule. No, not one of the good guys. Rava, of all people.
Danny Phantom: In "The Fenton Menace", Sam and Tucker can't see Youngblood when he's tormenting Danny even though the aforementioned himself establishes that he's only invisible to adults or kids who act like adults (like Jazz).
In the 200th episode of South Park, Stan says that he met Muhammad once, referencing the episode "Super Best Friends". In another episode "All About The Mormons", he does not know who Joseph Smith is despite the fact that he met him earlier in the same episode. Why would he remember Muhammad, but not Joseph Smith?
Patrick says in "Something Smells" he doesn't have a sister. Five seasons later in "Big Sister Sam", he has a sister named Sam.
In "Squilliam Returns", SpongeBob forgets his name since it is "emptied" from his mind, but after serving Squilliam, Squidward addresses SpongeBob by name, and he replies as if he already knows his name.
In "SB-129", SpongeBob for some reason never opens the freezer, even though there were frozen Krabby Patties in there.
In "Sleepy Time", Gary and Pearl are among those annoyed at SpongeBob for appearing in their dreams, but he didn't do anything in their dreams that inconvenienced them in any way.
In "To SquarePants or Not to SquarePants", SpongeBob's pants shrink in the wash and the store attendant tells him they're not expecting a new shipment of square pants for months. However, three days later (according to the episode's narration at the beginning), SpongeBob is wearing square pants again.
Filmation's Ghostbusters was well-known for structuring episodes based around an Aesop, but "The Girl Who Cried Vampire" is a case where the moral of the week results in a plot hole: in the story, a girl named Kita wants to have some fun, so she uses her ghost-like Scarecrow Balloons to attract the GB's attention. Here's the problem: the balloons trigger their Ghost Alarms even though they're not ghosts! And nobody thinks to question it!
One of the many challenges of Xiaolin Showdown ended with Jack losing but not giving up the Wu he had bet, neither he nor Omi seem to notice this.
In one episode, the Sands of Time - a time-travelling Shen Gong Wu - was taken by Old Omi back into his own time, 80 years into the future. In a later episode, Omi freezes himself for 80 years so that he may retrieve it. Only, this led to Omi being gone for 80 years, resulting in a Bad Future where Jack rules. So getting the Sands of time is going to be harder, as Jack has them in his safe... but it's never explained why the Sands of Time still exist at all when Old Omi doesn't.
Voltron Force- Larmina (a teenager) is stated to be Allura's niece. But in the original Western Animation/Voltron, Allura is an only child. Not only that, but not enough time has passed (only around 7 years at the very most) for Romelle (Allura's cousin) and Sven to have a teenage daughter. So who in the world are Larmina's parents? Being royalty and without heirs it is possible that Larmina is the daughter of a distant relative of Allura
Redakai: Despite having had a rather heated argument over common sense, the heroes automatically assume that the Face–Heel Turn of their comrade Maya is due to mind control (And not coercion, a clever plan of subterfuge, actual feelings of betrayal, or even just to teach them a lesson about how big jerks they are). Not only that, but they can tell who applied it and with what even though they did not witness the encounter nor have any recording of it. And just for fun, the attack (Named after the lead villain) infuses its target with evil, but apparently using it again cures the victim, rather than making the situation worse.
Star Wars: The Clone Wars in the Season 3 episode "Assasin" Aurra Sing was arrested for attemping to murder Padmé, and it's quickly discovered, that it was Ziro the Hutt who hired her for the job, because he wanted to get even with Padmé, for putting him in jail. This created two huge plot holes. A) How did Ziro hire a wanted Bounty Hunter, while in prison? Made even weirder by one of Ahsoka's earlier visions, which showed Aurra personally talking with the Hutt. Um... how did she get in the prison to talk to him? B) In the Season 1 finale "Hostage Crisis' Ziro was broken out of prison by a group of Bounty Hunters, Sing included. Since in "Assasin" Ziro was still in prison, it's obviously takes places prior to "Hostage Crisis". However Sing was arrested in "Assasin"...How did she get out by "Hostage Crisis"? This latter had been addressed by Word of God months after the episode aired, confirming the fan theory of Cad Banebreaking her out.
In the first Wakfu OVA, Count Harebourg gives Yugo an ultimatum to show him how to use the Eliatrope Dofus or he'll use the Sadida's forests as fuel for his furnace. However, no reason is given as to why he would use the Sadida's forests as an alternative when he already has a forest full of trees, which are renewable resources.
In Young Justice (2010) the League is brainwashed by the Light and sent off to wreak some havoc. They later discover that they have no memory of what they did and spend five years trying to find out, completely overlooking the possibility that they could ask the GL Corps, or even the ring itself. Even if they turned up to be a dead end, it's still a better place to ask around about the whereabouts or activities of a certain green clad ring-wearer than anywhere else, especially anywhere on Earth. Weisman completely dodged the question, making vague claims about the government of the attacked planet being corrupt, but it seems like one of their guys being Brainwashed and Crazy and in possession of the strongest weapon in the universe would be a big issue for the Guardians, regardless of whether the planet would tell them they were attacked.
Ned's Newt: In the pilot, Ned pays exactly $1.65 (all of the change in his piggy bank) for Newton; the pet store owner actually rips him off, because the price list said $1.49. However, in a later episode, Ned loses his "lucky penny", described as such because it was his change when he bought Newton, even though we were explicitly shown the original transaction.
X-Men: The Animated Series: Jean Grey departed after the Phoenix Saga in Season Three, and is treated as though she actually dies. However, two episodes afterwards, the Dark Phoenix Saga begins and she is treated as though she returned off-screen. What happened actually is that there are three episodes in Season 5 that should have aired in Season 3, one hinting about Jean's return. And yet no episode of Jean actually returning came to air.
In the already So Bad, It's GoodGrandma Got Run Over by a Reindeer Christmas special, Grandma doesn't die from being hit by Santa's sleigh (unlike what the song and its sequels—yes, it had sequels—imply) but was taken to the North Pole after losing her memory from a concussion. The plot hole comes in when it hits you that Grandma's been missing for nine months and Santa never thought to return her to her home; being Santa Claus, he should obviously have extensive knowledge of who everyone in the whole wide world is and after being declared missing Grandma's face was on various milk cartons, something you'd expect Santa to notice since milk is his favorite drink. Even ignoring all of that, he ran her over in the front lawn of a house: it doesn't take a genius to reason that's either her house, or the house of a friend, and to just drop in and ask for some information about her.
In The Secret of Mulan, Mulan dresses as a man in order to join the army. Yet Zhing Zhing appears to be part of the army, as the Prince asks her to report her findings to him, and nobody seems to care.
In "Fairly OddPet", Sparky buries Timmy's house underground, forcing Timmy to wish it back aboveground. However, when he tries to fix the rest of the town, Cosmo and Wanda tell him that Sparky buried their wands.
In "The Big Fairy Share Scare", Cosmo and Wanda are supposed to have lost their wands, yet at one point, Cosmo suddenly has his wand again long enough to produce a flashback sequence. It then disappears almost immediately afterwards.
Season 1 has a Halloween Episode where Shimmer and Shine are introduced to Zac as kids wearing genie costumes. Promotional material for Season 2 has a scene where Zac meets the genies again and learns the truth about them. For some reason, he's surprised that they know his name.
In "My Secret Genies", one of the things Shimmer and Shine magically conjure to convince Leah they're real genies is a treehouse. However, in "Genie Treehouse," they assume Leah means a house made of trees when Leah wishes for a treehouse.
In the What's New, Scooby-Doo? episode "Big Appetite in Little Tokyo" the Villain of the Week manages to build a giant robot monster version of Shaggy despite Shaggy not being his original intended target and having less than a day to change his plan. He also managed to hide the giant robot somehow.
