Maybe the characters are in another country, time, or even planet, but they fit well enough with Potter canon. Sometimes even complimenting it.

I like imagining Percy Jackson and the other Demigods existing in their own hidden world. The magic used isn’t crazy, and the Master of Death story can have real ties to Hades.

 

Most anything that's exclusively about muggles fits with HP.

 

Mary Poppins was one of Grindelwald's followers who believed in using magic for the good of Muggles.

 

Probably some of the classic gothic/horror fiction - Dracula, of course, and Frankenstein could be re-invented as being inspired by inferi or similar.

 

All the supposed alien UFO sightings were just some drunk wanker on a broom letting off sparks and strobe charms.

 

Now I'm just imagining a series of drabbles showing the reactions of various fictional world leaders to the news that magic is real.

From the reasonably calm and intellectual questioning of President Bartlet. To the panic and faffing of Prime Minister Hacker.

 

I can see this. I can even see a half-blood at Hogwarts, venturing out into the forbidden forest to battle mythological creatures for their spoils of war, which turn out to be hard-to-come-by potion ingredients or something. Slytherin was actually a half-blood and his monster was a Basilisk/Jörmungandr hybrid he was screwing around with.

I had this idea last summer...

Spoiler

"Why do I always end up with the nastiest spoils of war?"


Professor Snape finished conjuring the siphoning apparatus to several empty beakers below my latest trophy. Contained in the uppermost one was the hat of the Red Cap, dripping an almost constant flow of fresh blood collected over the centuries of its existence. I expected dozens of beakers to be filled once all was said and done. Needless to say, it was a very rare and highly expensive potion reagent. It was probably the sole reason the Professor put up with my truancies, my general disposition, and my occasional disheveled appearance, much like that night. At that point, I was dirt and blood stained, but my deity-gifted clothes were still intact and concealed beneath my standard outer robes.


While the heads of house had been briefed about my demigod status by my second year, the entirety of the student body, like the majority of the human race, were ignorant of the existence of people like me.


"Consider yourself fortunate." Professor Snape turned to his desk and opened one of the lowest drawers before retrieving a pouch of coins. "Your portion of this month's proceeds."


A quick examination of the material and I deduced it to be mokeskin, and after I reached inside to see its contents, I realized it had also been enchanted with an Undetectable Expansion Charm. After that I simply raised an eyebrow at him.


"Three hundred and seventy-four galleons for the powdered remains of Rawhide and Bloody Bones you dispatched two months ago." He motioned toward the beakers. "I estimate triple the amount for what you made available tonight... and that, Miss Rosier, is why you shouldn't bemoan your lot in life to always end up with the nastiest spoils of war."


Well, he had a point.


Once he secured the cabinet the hat and its contraption were stored in, he motioned to me. "You should, perhaps, consider opening a vault with the goblins. It would make the transfer of funds much simpler."


I shook my head before stashing the pouch in one of the inner pockets of my jacket. "For a decent price, Goblins gossip far too much. I don't need it getting around my net worth dramatically jumps right after rare reagents hit the market."


He narrowed his eyes at the implication that I would let him shoulder the entire burden of being the only person that knows where all the choicest of creatures are located. Most likely deducing, if someone was to take interest, a former Death Eater would be the one to turn to instead of a defenseless student. He would be correct.


Before any more was said, a timed yet urgent knocking came at the door.


"Come," Professor Snape called out.


A little Gryffindor firstie stuck his head in the door, reaching out his hand as far as it would go, lest he get too close to the bane of virtually all Potions students. A crumpled note was clutched in its grasp. "From the Headmaster, sir!"


The parchment was snatched from the firstie's hand and with a wave Professor Snape's own he was dismissed. A moment later a single eyebrow was raised and his attention was placed on me.


"The Headmaster requires your presence in his office."

 

Most horror films would work as just some muggles encountering some dark creature or spirit like boggart or poltergeist

 

100% Addams Family exists within the Harry Potter universe. I believe they're social outcasts in America, shunned for breeding with non-human beings and dabbling with very dark magic.

However, due to their considerable wealth and powerful wandless magic they've been given some freedoms regarding the Statute of Secrecy.

They're free to use whatever magic they want in front of muggles, as long as it isn't done with a wand (which the Addams' don't use anyway) and is done in the Addams Family manor.

 

I definitely read a crossover like this back in the day.

 

It's like peanut butter and chocolate, it goes together so well. The magic systems are very similar and the wacky characters of the Addams Family fit really well with the Potterverse whimsy.

 

I didn't see much of it, but a version of Warehouse 13 could fit. In that show, "agents" come across artifacts charged with powers (like Lewis Caroll's looking glass) and lock them away. I could imagine some of them as being magic artifacts and enchanted muggle items.

The Munsters could be a similar family to the Addams.

A version of Sleepy Hollow probably were the events leading to the creation of one of the ghosts of the Headless Hunt.

Scooby-Doo could be a gang who keeps coming across actual magical events but keep on getting Obliviated into thinking it was Old Man Jenkins.

Matilda could be an undiscovered Muggleborn who uses wandless magic.

Jumanji. The original, not the remakes.

 

Shezza wove the Denarian stuff pretty seamlessly and in a way that made sense to the HPverse. Still one of my fav HP fanfic to this day.

 

Charlie and the Chocolate Factory. Dementors have been breeding and to help the muggles out, the Ministry hatches a plot to widely encourage the consumption of chocolate. Except, some brainless ministry wizard actually did include golden tickets. Story ensues...

 

Monday Begins on Saturday by Boris Strugatsky.
Marvellous book, rarely read in the West, I knew of it mostly from being written by the same authors as A Roadside Picnic/ Stalker untill last year I finally read it. As I understand it, its a very popular novel in Russia. Its about Soviet Magic Scientists working at NITWITT (the National Institute for the Technology of Witchcraft and Thaumaturgy). Aboslutely loaded with parodies of folklore characters and bureaucratic wrangling. I mean, we know that some archaic states like Assyria and Transylvania still exist in the HP universe, why not the Soviet Union?

 

Hellraiser, as well as lot of Clive Barker's stuff in general. Philip LeMarchand - who made the LeMarchand boxes - turns out to be a wizard who was a dark version of Nicholas Flamel. Funnily enough, I do recall reading a few years ago a HP/Hellraiser fic where Harry defeats Voldemort by summoning Pinhead and the Cenobites.

 

That's an old, old Ruskbyte one. I remember reading it a few times... 15 years ago? Jesus fuck.

https://www.fanfiction.net/s/2452681/1/Evil-Be-Thou-My-Good

 

The idea's been kicked around before.

Spoiler

EDIT: Placed the images in spoilers due to length.

 

Scooby Doo.

 

I read this fic every few years as a tradition. That's how good it is.