Supernatural's 2018 episode "Scoobynatural" bizarrely, but successfully, brought together the monster-fighting worlds of the Winchester brothers and Scooby-Doo. Both properties are owned by Warner Bros., which, according to Supernatural executive producer Andrew Dabb, made the oddball idea an easier pitch on the grounds of "corporate synergy."

On paper, the animated "Scoobynatural" wasn't an immediately obvious choice for Supernatural's first official crossover. In practice, however, the chosen professions of Mystery Inc. and the Winchester brothers correlated enough to make the premise work, even if the spooky things that Shaggy, Scooby and the others investigate are usually just real-estate scammers in Halloween costumes rather than the very real terrors that Sam and Dean have to deal with.

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Beyond that, the essences of both properties were distilled together, rather than diluted, in the merger: The Winchesters zigzag through a haunted house and get to eat giant sandwiches, while the Scooby Gang looks past a bloody crime scene with peppy, '60s cheer, and later have a collective nervous breakdown upon the discovery that monsters really exist.

"Scoobynatural" remains one of Supernatural's highest-rated episodes among both critics and audiences. Less successful, and less remembered, is the show's actual first crossover (of sorts), which is even wackier than Sam, Dean and Castiel being sucked into a 2D cartoon world.

After softly introducing fairies into the series' canon in seasons 6 and 8, Season 9's "Slumber Party" revealed the show's world also contains leprechauns, elves and the existence of an entire fairy realm called Avalon, where the land of Oz exist.

And yes, that's the Oz from The Wizard of Oz.

The boys, along with their go-to tech support, Charlie Bradbury (Felicia Day), make this surprising discovery when they accidentally free Dorothy -- the Dorothy -- from a decades-old mystical barrier created to stop the Wicked Witch (of the West, we presume) from crossing over into our world. This Dorothy is the daughter of author L. Frank Baum, whose books were actually written to chronicle his daughter's real adventures in the fairy dimension.

In an effort to blend Oz and Supernatural lore, the show makes Baum a member of the Men of Letters -- the covert, international organization that researches and tracks the supernatural -- and Dorothy a hunter. It's believable enough, but not enough to make this episode hang together as well as "Scoobynatural" does.

A big part of the problem is that this "crossover" couldn't be an official one. Despite Baum's original book, published over a century ago now, being within the public domain, the franchise that was born from it is a minefield of competing corporate interests fighting to stake their claim. (The copyright status of the various Oz-related media is so messy, it has its own Wikipedia page.) Warner Bros. actually owns the iconic 1939 film, and yet, Oz iconography is still oddly restrained in "Slumber Party."

Rather than send Sam and Dean into Emerald City -- as you'd hope in a Wizard of Oz homage and was the pivotal appeal of "Scoobynatural" -- the episode instead forcibly inserts Baum's colorful characters into the grubby world of Supernatural. However, it's never quite able to scrub the shimmering pixie dust off them, although the Wicked Witch's stony-gray makeover is decently spooky.

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Rather than immersing us somewhere new, the episode can only let us glimpse the Yellow Brick Road from a distance as Charlie steps through the portal linking the fairy dimension to ours, skipping off hand in hand with Dorothy to embark on an adventure that takes place entirely off-screen.

Budgetary constraints no doubt factored in here, but considering the series has conjured serviceable illusions of heaven and hell from well-decorated single rooms, you'd think dressing a few extras in green and cranking up the Technicolor wouldn't have broken The CW's bank.

Having said that, even if we had gotten to see Sam and Dean dozing off in a poppy field and (inevitably) calling the Wizard a jerk, it wouldn't have actually solved the other underlying problem: Supernatural and Oz just aren't a comfortable fit.

Like most fairy stories, Baum's original books are much darker and weirder than the bright-and-shiny version of Oz that Hollywood made famous. However, the shimmering big-screen version of Oz  is such a difficult idea to dislodge that it's still hard to accept something as horror-influenced as Supernatural -- for all its moments of silliness -- gels at all with a world where tyrannical witches can be thwarted by buckets of water.

The episode tries to eschew this disparity by having Dorothy explain that her father "got the mythology all wrong" in his writing. Regardless, using a relatively modern fantasy property as the basis for a storyline is a jarring shift from the religious lore and ancient myths that the show usually relies on. Supernatural's unofficial Oz crossover remains one of its strangest moments -- and that's really saying something when you remember that one time Dean shot Hitler.

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