After getting picked up by The CW, The Winchesters has given Supernatural fans another excuse to rewatch fifteen seasons worth of the series, with many fans happy to sit through most episodes even if they are not as good as the best or if they are deemed filler. Filler can be hard to define, especially for a show like Supernatural with its early monster-of-the-week structure.
Nevertheless, there are some episodes beyond those first two seasons - which are primarily monster-of-the-week episodes - that are clearly filler (which here can be defined by them not impacting or tying into the overall story of the season nor adding anything new to the characters) but are great anyway.
Monster Movie
Season 4 Episode 6
"Monster Movie" is a classic monster-of-the-week style Supernatural episode that may well be one of the show's most underrated, perhaps lost to time under the rubble of classic meta-stories and emotionally affecting forty-five-minute narratives.
It is an ode to classic horror movies and a unique creative endeavor, entirely done in black and white as the brothers battle a shapeshifter that impersonates the classic horror villains of old such as Dracula and the Werewolf. The story of season 4 is not impacted by the episode, and its absence would not alter the direction of the series at all. It is just an incredibly fun bit of Supernatural TV.
The Curious Case Of Dean Winchester
Season 5 Episode 7
Compared to seasons 1-3 especially, season 5 does not have too much filler, with most episodes tying in some way or another to the main storyline of the Apocalypse. "The Curious Case Of Dean Winchester" is an exception, though.
This is a fantastic Bobby episode, but it is not as if it changes his character or has a long-term effect on his role, he shines in his relationship with the brothers as he does in so many other episodes. Instead, it is a fun story that sees the Winchesters try and take down a Witch who has a surprisingly emotional ending. The dynamic between old-man Dean and Bobby is legendary and some of the funniest Supernatural ever.
Yellow Fever
Season 4 Episode 6
Undoubtedly one of Supernatural's most iconic episodes is "Yellow Fever." So much of that is down to Dean Winchester and the performance of Jensen Ackles, which fans will remember for a long time.
The episode follows Sam and Dean on a typical ghost hunt, with the added twist of ghost sickness. Dean contracts it, leading to one of the most famous Supernatural moments, Dean's scream at the cat. This episode could not exist, and the show's story would not change one modicum, but it would be worse off overall because the world would be deprived of Dean's "Eye of the Tiger" rendition.
LARP And The Real Girl
Season 8 Episode 11
Supernatural is pretty much built on its character dynamics, but it is not just the typical Sam/Dean and Dean/Cas relationships that are incredible, there are others too, such as that between Dean and Charlie, which shines in this episode.
The entry into the series is just fantastic fun. There are not a ton of stakes, and the overall plot of season 8 is not affected. The only real arguable long-term effect is the beautiful friendship between Charlie and Dean developing. Fans are happy the episode exists for Sam and Dean's LARPing, if nothing else.
Regarding Dean
Season 12 Episode 11
Jensen Ackles and Jared Padalecki continuously prove their skills as actors throughout Supernatural. Still, as far as individual performances go, Jensen is utterly phenomenal in "Regarding Dean," arguably the best performance in the show and one of Dean's standout individual episodes.
Following Dean, as he loses his memory, which Sam and Rowena attempt to bring back, Dean is both hilarious and heartbreakingly vulnerable at points in the episode. The dynamic between Dean and Rowena is also great here, while the Sam and Rowena relationship shines as it always does throughout the show. The episode has no long-term impact on the story but a huge impact on fans who will always remember that mirror scene.
Mint Condition
Season 14 Episode 4
The later seasons of Supernatural fall away from the early season monster-of-the-week style in favor of more interconnecting episodes and myth-arcs, but there are still some gems as the show winds down, including this ode to slasher horror.
'Mint Condition' takes the concept of action figures coming to life - far from the weirdest things the Winchesters have hunted - and puts the heroes in a horror film, giving audiences a hugely fun, inconsequential treat. This episode will be especially enjoyable to fans of cheesy, classic slasher horror, even if it, for obvious reasons, lacks the gore of some of those beloved films.
Wishful Thinking
Season 4 Episode 8
Whereas many shows falter when they attempt to be as wacky, as meta, or as ridiculous as possible, this is often where Supernatural shines the most. A great example of this is "Wishful Thinking" which will stick in the memory of fans for a long time.
It is a great contained story about wishes coming true thanks to a cursed coin and a wishing well, but the memorability factor comes from the giant teddy bear who comes to life and turns into a cynical and suicidal alcohol abuser. Dean and Sam are great in amongst the ridiculousness, which also includes Sam getting struck by lightning and Dean getting overpowered by a small child.
Dog Dean Afternoon
Season 9 Episode 5
As is the case with many of Supernatural's weirder stories, "Dog Dean Afternoon" is definitely not for everyone. However, those fans who like it often view it as one of the best standalone episodes the show has to offer.
Following murders to which a dog was the only witness, Sam and Dean perform a spell to communicate with the dog that leads to Dean becoming a dog in his mannerisms. It is hilarious. From Sam's reveling in what is happening to Dean to Dean's communication with the animals to his dynamic with The Colonel, the episode is better than it has any right to be.
Scoobynatural
Season 13 Episode 16
Strangely enough, in the later seasons, it appears as though Supernatural was consistently better at weird, seemingly unachievable (qualitatively speaking) filler episodes than overarching, season-long stories, and "ScoobyNatural" is perfect evidence of that.
There is a fleeting mention of the ongoing plot of the season in the episode through Cas' romance with the Djinn, but apart from that, the episode is pure filler and one of Supernatural's best episodes. Removing it would not change the show, but it would certainly be a loss to fans. The twist on the classic Scooby-Doo episode is brilliantly done, and it is amazing how seamlessly Sam, Dean, and Cas fit in with the Scooby-gang and form dynamics with them.
Baby
Season 11 Episode 4
When it comes to episodes that have no effect on the plot of their season or even on the show's story overall, there is no episode better than "Baby," which, while not affecting the narrative of Supernatural, truly encapsulates what the overall story is.
Filler is often wrongfully associated with episodes that people may not like, but episodes like "Baby" are examples of what filler can be; not essential to the plot of the season (which in this case revolves around the Darkness) but arguably essential viewing to fans, many of whom believe this to be the show's magnum opus. From the 'Night Moves' sequence to Jensen's driving action to the quiet conversation between the brothers to the rightful appreciation for the Impala, this episode is what Supernatural is all about, and it is a joy to watch over and over again, even if it is 'filler.'