When I saw the Season 6 Finale of Dexter, I thought of "jumping the shark." John Hein coined this phrase after watching the episode of Happy Days where the Fonz literally jumps over a shark (or rather a portion of water that has a shark in it) while water-skiing. The episode marked the show's peak in quality and the clear beginning of a decline toward episodes that became gimmicky imitations of their former selves. The phrase has evolved and I believe it can be applied to some shows in and around my era of television. These shows are not related to each other but are familiar to many and have had significant impacts on popular culture (Scrubs might be an exception).
Season 6 of Dexter ended with Dexter's adopted police lieutenant sister discovering that he is a serial killer or at least a killer by witnessing him killing another serial killer/the antagonist of Season 6. The writers really only have a few options at this point. They could have Dexter's sister, Deb, accept him as a serial killer and work with him. However, this would not be consistent with her character since she has always been an incorruptible and clean cop. The other option is for them to have Dexter somehow weasel out of being caught, perhaps by lying and telling Deb that it was a one time killing. Ultimately, I think the show is doomed to go downhill since the writers must now change the dynamic of the show in order to continue it. People said similar things when Rita died but I think the show was able to continue on successfully. Now I'm not so sure. I'm going to dive into the 8th Season once I have time but I feel confident in my prediction and have already heard whispers of drastic changes.
It was pretty clear that Supernatural had peaked after the main characters literally re-sealed Lucifer in hell after four seasons of slowly building up to his release and then the entire 5th Season spent stopping him from unleashing the apocalypse. After all, what could be more epic than beating the Devil? The writers failed to answer this rhetorical question in the following seasons. Seasons 6 and 7 had some cool moments like Castiel, the Winchester Brothers' Angel buddy, sort of becoming God and a hilarious episode about Sam's fear of clowns but Season 6 didn't really have much of a continuous thread to the plot and Season 7...come on...Leviathons that possess people by eating them like in The Invasion (the crappy one with Nicole Kidman not the classic which is also crappy). The show has started an 8th Season and I'm probably not going to watch it. Probably...fine I'm going to watch it.
There are conflicting arguments as to when the Dragonball Trilogy jumped the shark. Some say that producers never should have made Dragonball GT and others say that the show jumped the shark after the Frieza Saga in Dragonal Ball Z. I have to side with the latter. There were some epic moments in the Androids and Buu Sagas but the fight between Goku and Freiza was epic and amazing to the point where all of the subsequent fights in the series seemed underwhelming even though the villains were supposedly stronger. Frieza was looked back upon as being weak even though he basically ruled most of the known universe and had the most history with all of the main characters. Things that began as a huge deal such as becoming a Super Saiyan also became unimportant, especially once Trunks and Goten became Super Saiyans as eight year olds. Characters that were once respectable such as Piccolo, Krillin and Tien became comic relief or background characters (I was going to say Yamcha but he was always worthless, even in Dragonball). In my opinion, the main thing that kept Dragonball Z interesting and engaging after the Frieza Saga was the dynamic between Goku and Vegeta, especially during the Buu Saga.
Scrubs most obviously jumped the shark since they continued after the "Series Finale." It was thoroughly advertised as a "Series Finale" and ended with the main character, JD, walking down a hallway and saying goodbye to every single supporting character that they could get to do a guest appearance. However, I was surprised and more than a little pissed off to see promos for Scrubs Season 9 the following summer. Of course, it was terrible. Characters like Carla and The Janitor completely disappeared and focus drifted away from characters like JD and onto new, crappy characters. Zach Braff even admitted in interviews that the writers were using his character during the beginning of the season in order to help the fans stomach the new characters long enough for them re-commit to the show. Season 9 was the last season and thanks to ABC Scrubs had to trade its awesome "Series Finale" for a terrible Series Finale.
I did not see the 1986 movie when it came out but I still watched Optimus Prime get gunned down on VHS after renting every single episode of the prior seasons from Hollywood Video. I don't know what the writers were thinking when they decided to kill him off but it was obviously a terrible decision. The producers faced thousands of angry letters from fans and parents saying that their children had been irreparably traumatized. They also doomed the new leader of the Autobots, Rodimus Prime aka Hot Rod, to be hated by fans since he caused Optimus' death by interfering with his fight with Megatron. The show took a sharp downfall after Prime's death and never truly recovered even after they revived him numerous times.