Plot hole: In the pilot, it is established that the surface of anything/anyone made invisible by "quicksilver" is freezing. (Darien gets caught in the women's shower because the mist freezes on him. He freezes the beer mugs for the doctors.) But in later episodes, nobody notices him standing invisible - and freezing!? - next to them.
Plot hole: Dillon was quickly identified by the city sensors as having metal parts, thus classifying him as a threat to the city. Yet Tenaya, who is essentially a cyborg, tries out for the Green Ranger without setting off the same sensors.
Suggested correction: Tenaya wasn't caught because the guards assumed the equipment was faulty. It was giving positives all day because of all the sleeper agents we find out about later.
Molly's Neverending Story - S5-E5
Plot hole: At the very end, Molly gives Peggy's church friends each a gift for their advice with changes she made to her book. Peggy says, "You didn't really need their notes, it was already a very good read." The problem is, there's no way she could have made any changes from the time she talked to them to the time Mike sends the email to the publisher. Molly actually says from the closet, "They wanted me to take my book to a dark, dark place." When did she actually incorporate their notes?
Plot hole: When Connie uses the wish machine to make Malloy small again, she instead wished for Ethel's breasts to get significantly bigger. However, in the next scene Ethel's breasts are back to her regular size. The plot shows that the wish doesn't wear off, and someone else would have needed to wish for Ethel's breast to get smaller but no one did.
Farewell My Beloved Witch - S1-E3
Plot hole: Lupin was captured by chance, and he did not plan for that, nor he seemed to have previous knowledge of Stern's appearance, but he escapes regardless using a Mission Impossible-like perfect mask of him. He also somehow kept his own blazer, tie and shoes underneath the uniform and boots he stole and wore. (00:16:00)
Plot hole: In the episode "Scheming Schemers" (1956 - fake Shemp episode) at the start of the episode, Moe is given the address for a plumbing job over the phone and he and Larry take off in their jeep - accidentally leaving Shemp behind. Next scene, Moe and Larry are in the house working on their plumbing job and minutes later Shemp just shows up outside in a separate vehicle. Shemp would not have known where the job is since he was left behind and never would have known the address Moe and Larry went to.
The Marathon - S4-E3
Plot hole: Jason cheated in three different ways in order to beat Aurelius in The Marathon, and admitted it. So the bet that they made between them is null and void. But the last shot shows them living up to the terms, which includes Aurelius starting to eat his own shit (literally), so revolted that he's trembling. Apparently the writers really really wanted to include coprophagy. But who would eat faeces for a bet, if you can simply avoid it by reminding your opponent that he cheated? Or even better, many would say that cheating means losing automatically, so he's the one who should be eating his own shit.
Plot hole: The whole episode is based on false facts. Cody was getting an A in woodwork and Zack was failing in all his classes the previous year at school (according to their report cards in Ep "Smarter and Smarter"). So Cody knows a lot more about woodwork than Zack and should be able to make a clock, never mind a birdhouse, and Zack should not be able to make a clock.
Into the Mouth of Evil - S2-E23
Plot hole: While fleeing the guru's disciples through a narrow side street, Jackie gets cut off by the van driven by Dr. Jamba and associates, stun-sprayed in the face, and then loaded into the van. But with three brutish-looking guys being so close to their quarry, the real crooks can take the time for dragging Jackie around to the back door instead of loading him through the side doors?
Plot hole: When the watch is sucked to the island by the magnet, where was the sailor that the watch was attached to?
Plot hole: The plot hinges on Kimmy finding evidence against Pastor Wayne inside of the bunker, which she ends up doing. But there's absolutely no way the police didn't thoroughly comb the bunker for evidence after discovering it. In fact, it looks like it's barely been touched in the several months that have passed. Yes, the show has a sort-of whimsical "cartoon" logic... But even in that way, it makes no sense whatsoever.
Hone made aishite? Akane koi o fukuzatsu kossetsu - S1-E5
Plot hole: Dr. Tofu is able to tell that Ranma was hit by a softball (he says something about the marks like he actually sees them), but Ranma's wound is still covered by the bandage, that he'll remove in the next episode. This is linked to a larger mistake in the following episode. (00:19:55)
Plot hole: The Jupiter 2 crew is duplicated; however, the aliens had never seen Penny (or Judy I think). How can they be duplicated? The aliens don't have ability to know who were there, or they wouldn't have questioned Smith about the crew. Also, they do not know Smith and Will are hiding. So, they don't arm to have any special power to know beyond what they actually observe.
Deathfist 5: Major Crimes Unit - S2-E15
Plot hole: The whole case is solved because of astronomical coincidences, since the culprit is someone related to the actor, who is teaming up with the investigators for an entirely unrelated reason. Los Angeles is kinda too big for this sort of 'coincidence'. Moreover, had they committed the crime any other day (there was no particular reason) there would have been no connection.
Plot hole: Rick is taking care of his girlfriend's goat for a few days. He puts a bowl of milk on the floor, but The Goat will not drink. Harriet suggests, "We're probably just using the wrong method." The next scene shows Ozzie at the stove, heating milk in a baby bottle. Rick is 22 years old. Why would Ozzie and Harriet still have a baby bottle in the house?
Plot hole: In Russia, Soldier Boy is shown heading to the airport, He wanted to get to the US and start his revenge against his team. Problem is: he has no documentation and money to take a flight. Even if he stole the money somewhere, still would be impossible to travel without the proper documents.
Happy Birthday... Everybody - S3-E20
Plot hole: After a chance meeting in Mexico, Tom Matthews invites Kelly and Scott to his home for dinner. The address is unlisted, neither knows where the other lives or is staying, and no address or phone information is exchanged before they part. But Kelly and Scott somehow find the house anyway. (00:09:50)
The Muh-Muh-Muh-Murder - S1-E25
Plot hole: Daffy isn't able to escape Porky's house until he gets the keys, but later it is revealed that the reason he couldn't get out was because he was too weak to open the door. If that was the case, the keys shouldn't have been able to help him get out.