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In All Hell Breaks Loose, John manages to stroll out of hell, saves Dean from getting shot by Azazel, give his boys an 'I'm proud of you' look, and goes up to heaven in a cheap white light. Nice, if slightly cheesy, right? Wrong. Dean's going to be in hell for a shorter time than he was and suffer PTSD when he gets out; there's no way he should be fine. Sam just gets a stiff nod (which doesn't exactly make up for him being sent for coffee in My Time Of Dying). The boys don't have much to be proud of. Dean gets to commit suicide, Sam's killed a human in cold blood, and Bobby and Ellen got to close the gate while they were pinned to a grave and a tree. They've made clear that John's a terrible father who has messed them up horrifically badly. So you can be forgiven for either feeling completely frustrated or having a bitter taste in your mouth. (This might have been intentional; you can never tell with this show.)
When it comes to John, there tends to be a lot of (maybe intentional, seeing how they think he's a psychopath) wallbangers. Like Long Distance Caller, for example: Dean had a beautiful revelation that John was an arsehole, and now he's back to "I made that deal 'cos you told me to look after Sam and I'm sorry, please don't be mad at me"; and Sam is completely disbelieving anything his father (or a reasonable facsimile thereof) says. Oh John, why are you still fucking up their lives so much?
Dream a Little Dream of Me. The villain became a psychotic killer because he couldn't dream.
REM sleep holds the psyche together, and the villain had an abusive father. This is not a stretch. If anything's off, it's the fact that he has long-term memory.
There are conditions that prevent REM sleep, and the people with them function reasonably normally. It's just that the majority of people need to dream.
Season 3 in general: Executive Meddling forced the show to introduce two new female leads in the third season. Instead of attempting to integrate them into the show's premise, Kripke insisted that they be kept separate, supporting characters and that the focus remain on the Winchesters. Which isn't, by itself, a bad decision, why change a working formula? The problem was that constantly shoehorning the girls, particularily Bela, into episodes became somewhat contrived. Bela kept randomly showing up, and, while Ruby was written as morally ambiguous, Bela was just plain not on the Winchester's side and tried to kill them several times, and generally contributed little to the show.
After the Wallbangers in Season 3, Season 4 bounced back by producing some of the show's best episodes - until the 10th episode. "Heaven And Hell" had several Series Continuity Errorswithin the same episode, most notably the idea that angels can't feel or show emotion, despite a large amount of emoting by the actors. Then they decided to include a contrived plotline with "fallen angel" Anna, complete with a schmaltzy Titanic homage. Some are of the opinion that if not for the Tear JerkerDowner Ending, the episode would have been a complete waste. There is plenty of snark to be had, but nothing does it justice like the TWoP recap.
The "pep talk" at the end of "It's A Terrible Life", where the angel tells Dean to stop whining about his life because he has a cool car and can sleep with hot women. Say what, writers? If you feel like that, then why put so much effort into breaking the cutie in the first place?
Well, given that said angel was Zachariah and was egging Dean on, the writers probably meant the opposite of that.
When Anna goes back in time to kill Sam and Dean's parents... shouldn't both she and Castiel have known that such a plan was doomed from the start, since Castiel deliberately sent Dean back to a place where he would screw things up if time could be changed?
Actually, Season 6 makes it canon that Angels at the very least can change the future if they themselves paticipate in the events (like how Balthazar prevented the Titanic from sinking since he was on the ship).
The time travel episodes are pretty pointless, in general, especially after they establish that you can't change the past. Also, it makes no sense that the de-powered season five Cas (who can't even heal people) is able to transport three people back in time.
There are a number of episodes which rely so heavily on idiot plots that they are painful to watch. "Weekend at Bobby's" strikes me as the absolute worst, since doesn't just involve Dean doing something stupid (which is to be expected), but also Bobby, who has common sense. And in the episode "Swap Meat", how could it have taken Dean so long to realise that Sam had switched bodies with a high-schooler?
Why didn't the angels fix Pamela's eye-sight, after Cas accidentally blinded her? It just seems like really bad PR, especially considering that, at that time, the angels were trying to prove to the brothers that they were the good guys.
Castiel needs Dean, Sam and Bobby out of the way so he can break into Purgatory. We've seen on many, many occasions that he can teleport people great distances, or render them instantly unconscious with a touch. So to ensure they don't derail his plans he... breaks the wall in Sam's mind, assuming this will be enough to keep the three of them occupied (not-a-spoiler: it isn't.)
Presumably, Cas figured that such things as temporarily knocking them out and teleporting them would be ineffective. He also needed leverage to hold over them, as he said when he was finished, he'd fix Sam.
It should be noted that the three of them ended up being unable to do anything to stop Castiel from opening up Purgatory. Sam being down definitely slowed them down a little, if not much.
Also presumably, since Dean single-mindedly focuses on Sam when Sam's in trouble and Castiel knows this better than anyone, he thought that was the surest way to keep Dean occupied. Those other methods just leave an angry group putting everything into finding and stopping him. And/or he really felt like hurting them.
In Season 6, how can Crowley not be prepared for Castiel to double-cross him? He should have had some contingency plan in place for such an event, especially after Castiel started threatening him about harming the Winchesters. For that matter, why does Crowley need Castiel in the first place? What did Castiel do to move the plan for finding Purgatory forward?
Dean spends the last few episodes of season six berating Cas for working with Crowley, on the grounds that Castiel should have come to Sam and Dean for help. However, once Castiel absorbs the souls in Purgatory and becomes a God, the first thing Dean does is work with Crowley to get the binding spell for Death. So... it's okay for Dean to work with demons, but not Cas?
Dean's worked with Crowley before as well, when trying to stop the Apocalypse. For that matter, he worked with Meg when trying to stop Crowley. Dean can be a real hypocrite.
Dean kills Amy in the "The Girl Next Door", a perfectly harmless kitsune on the grounds of 'she'll kill again'. Nevermind that she only killed to cure her son's illness-and even then, she targeted drug dealers and thieves, leaving innocent people alone.
No, what makes this a Wall Banger is that he leaves the kid alive. This was the absolute worst decision he could have made. The kid got sick from eating dead brains, which meant he'd probably get sick again before he finished growing up, which means the mom would probably go on another killing spree. Minimal casualties, but some casualties. If he'd killed them both, there would be no more murders, period. But now that the kid is alive, and has no more access to dead brains? How is he supposed to live without killing? Nice Job Breaking It, Hero.
Exactly how hard would it have been for Dean to tell Sam "I trust Benny because he saved Cas' life", thus avoiding half of the pointless drama at the start of Season 8? Sam would have immediately understood, and yet...
Sam's dislike of Benny is a wall banger in itself. He has no rational reason to dislike him. He keeps insisting that "He's a vampire!", but they've encountered good vampires in the past and Benny isn't hurting anyone. Furthermore, in just about every other situation involving a "good" monster, Sam is the one who defends the monster to Dean (Amy, Kate, Lenore, etc.) so he certainly knows it's possible for a vampire to be good. Some people have Fan Wanked Sam having hidden motives like jealousy over his bond with Dean or guilt that Benny helped Dean get out of Purgatory and Sam didn't, but this is never said in canon. Apparently we're just supposed to forget all the times Sam's been fine with monsters and accept that this one who's been saving Dean and Castiel's asses for the last year is evil just because he says so.
The whole last half of Remember the Titans was just cringeworthy. First off, Artemis is the goddess of the hunt, which would've made her relationship with the Winchesters fascinating to explore. In addition, she's the goddess of virginity and she's rather infamous for her hatred of men. And yet the writers, in all their brilliance, made her into The Dragon of the episode's villain. And then they made her into a love interest to Prometheus. The goddess of virginity is demoted to a love interest. To top it all off, they had her kill Zeus. Zeus. Sorry, what?
Yes, Dean, by all means, let the angel who explicitly says he's going to use Sam as a living battery possess him. He's been vouched for by Castiel, after all, and as we all know, Cas is the best judge of character. Always.