Harry Potter/Fanfic Recs/Crossover

These are recommendations made by Tropers for Harry Potter Crossover fanfic, all of which have to be signed to stay on the page. Feel free to add a fanfic of your own to the list, but remember to use the template found here.

You can also add to the current recommendations if you want. Refrain from posting Conversation in the Main Page though; that goes in the discussion page.

Harry Mewter by Alex Ultra
 * Recommended by lindabhair
 * Crossover with Pokémon.
 * Synopsis: Late in his second year, Harry Potter takes an animagus potion. His animagus form is Mew. Hilarity Ensues as he discovers catnip, learns what his new form can do the hard way, and tries to find out what the hell he turns into, anyway.

Harry Potter and the Digimon Frontier
 * Recommended by Ananonymuscat
 * Crossover with Digimon Frontier.
 * Synopsis: For five years, the kids of Frontier have been training as Japanese wizards. Now they've got the chance to study abroad, in England of all places. But there are some odd things happening. Digimon...at Hogwarts?
 * Comments: Don't let the title fool you, inspired by The Best Defense, this is one of the most thought out crossovers you are likely to find, everyone is in character, and the plot makes perfect sense.

Path of Decision by lulu42 (contains mild violence.)
 * Recommended by Fenro
 * Crossover with The Sandman.
 * Synopsis: Voldemort is in power, but the Wizarding World fights back. Harry Potter, Master of Death, is faced with a choice: move forward or change everything?
 * Comments: The plot is very intriguing, but there are a lot of spelling and grammar mistakes. This story takes place during Harry's Hogwarts years. This story is complete.

Invert by Marz1
 * Recommended by Fenro
 * Crossover with Fullmetal Alchemist.
 * Synopsis: While investigating a bizarre alchemical structure, the Elric brothers get pulled into the Potterverse early on in an AU version of Deathly Hallows. In the interest of finding a way home, Ed lends his talents to the Horcrux hunt while Al finds ways to keep himself busy at Hogwarts. Better than it sounds.
 * Comments: This was the fic that originally got me interested in FMA. It doesn't measure up to fics like Harry Potter and the Nightmares of Future Past or Dumbledore's Army and the Year of Darkness, but it's still an entertaining read. Seems to be a deadfic but the first half of the story is complete enough to enjoy as a stand-alone fic.

Cerulean Silver vs Amber Gold by hikaranko
 * Recommended by eagle108
 * Crossover with Fullmetal Alchemist.
 * Pairing(s): Draco/Hermione
 * Snyposis: Edward Elric gets assigned ...to babysitting Draco Malfoy, at the request of the British Ministry of Magic. While Ed considers the assignment stupid, having to spend an entire year undercover as a student at Hogwarts, there's a lot more than what he was told during briefing.
 * Comments: Excellently written, spot-on characterization, even with the deviations in the HP world. While the gradually built Draco/Hermione romance occurs in the background rather subtly to Ed's interactions with the HP cast as the main focus, it nonetheless has a strong and supportive impact in a whole to the story. Shades of Draco in Leather Pants is featured, but it's done quite tastefully. Ed here has a few "magic doesn't exist/magic breaks the laws of alchemy" moments but it's far and few in between, and he does comes to explanations that could work between both verses.

Dangerous Gifts by SGCbearclub
 * Recommended by Fenro
 * Crossover with Labyrinth
 * Pairing(s): Jareth/Sarah and SS/HG
 * Synopsis: Snape never asked to be rescued. Sarah never asked for magic. Jareth doesn't generally ask, period. The Ministry should have remembered that, back when they assumed they won the Goblin Wars. Nothing is ever what it seems. The story takes place after DH but without the epilogue. Labyrinth crossover.
 * Comments: There is a lot of Sarah/Snape interaction, but my most favored part, is the interactions between Jareth/Snape. One thing that was brought to my attention, was that I needed to do a bit of research on mythology in order to fully comprehend the story. This fic is rated M for Sexual Situations, Suggestive Themes, Violence, and mild-language. The last update was in March 2009.

Fusion of Destinies by Grey-X
 * Recommended by: SAMAS
 * Crossover with Metroid.
 * Synopsis: A blazing meteorite falls into the forest around Hogwarts, leaving an amnesiac woman called Samantha. Working odd jobs around the school, she finds herself drawn to Harry. But she's here for a reason: A terrible spell that has called forth a weapon from the future... and the one person that can stop it. Crossover with, of all things, Metroid.

If Wishes Were Thestrals, We'd All Run Screaming by Susan Anthony (Crossover with Harry Potter)
 * Crossover with Buffy the Vampire Slayer.
 * Recommended by User:Looney Toons
 * Synopsis: "Xander makes a wish and the Wizarding World will never be the same." Xander and Harry Potter switch places, altering reality, and Xander and Willow are the only ones who know it.
 * Comments:

Strange Bedfellows by MST3KguruK10 & Mrs Hyde
 * Recommended by Revlid
 * Crossover with Once Upon a Time In Mexico.
 * Synopsis: "We all need someone we can lean on..." Two unlikely men in an unlikely place find an unlikely friendship in each other. A post-DH, post-Once Upon a Time in Mexico crossover AU featuring Severus Snape and Sheldon Sands.
 * Comments: Yes, it's a Harry Potter, Once Upon a Time in Mexico crossover. No, I have no idea how that idea came about. Yes, it is pretty awesome.

Evil Be Thou My Good by Ruskbyte (AU, or maybe not if you consider the original setting of the, ahem, crossed material. Horror,Crossover, Dark!Harry, Disturbing, Disturbing, DISTURBING. HAHAHAHAHAHAHA!)
 * Recommended by Crackers don't matter.
 * Synopsis: Uncle Vernon thought to bring home a puzzle toy he bought to encourage Dudley's mental stimulation. A box shaped puzzle. A box that plays music. A young Harry solves the puzzle, and alone survives the consequences, to make it quick. Except now he can't stop thinking about the box, about that tune. And he's gained the attention of a very powerful dark being who is not a wizard. The sequel All Problems Solved is incredibly good as well.

The Flat Next Door by Tassos
 * Recommended by User:Looney Toons
 * Crossover with Buffy the Vampire Slayer.
 * Synopsis: In an alternate summer after the events of Order of the Phoenix, Harry and the Dursleys are moved by the Order into an apartment when 4 Privet Drive is identified and targeted by the Death Eaters. Harry finds little to recommend the change until he meets the gentleman living in the next apartment—one Mr. Rupert Giles, whose quiet and respectful friendship saves Harry's sanity and soul from the depths of despair.
 * Comments: Set after the final episode of BTVS and featuring almost none of the other characters from the series, this is a low-key story that nonetheless carries an unexpected emotional intensity, all the way to its quietly surprising ending.

Browncoat, Green Eyes by nonjon
 * Recommended by User:Looney Toons
 * Crossover with Firefly (post-Serenity)
 * Synopsis: Two years have passed since the secret of the planet Miranda got broadcast across the whole 'verse in 2518. The crew of Serenity finally hires a new pilot, but he's a bit peculiar.
 * Comments:

Of Gods and Men by shadowphantomness
 * Recommended by feral
 * Crossover with Death Note
 * Pairing(s): Light/Mikami
 * Synopsis: AU, The Death Eaters bite off a bit more than they can chew when they go after Kira.
 * Comments: Starring Light Yagami and Teru Mikami of Death Note with guest appearances by Harry Potter characters. Let's see, you got Magnificent Bastardry, Evil Versus Evil, and a chance to . Also watch for Funny Aneurysm Moments.

Itachi and the Prisoner of Azkaban by Mistress Dragonflame
 * Recommended by melloncollie
 * Crossover with Naruto
 * Synopsis: This fic is an Itachi-centric crossover with the Potterverse. While an ANBU captain, Itachi is called away to Britain on a mission as Harry Potter's covert bodyguard. Hilarity Ensues.
 * Comments: This fic could use a bit of polishing, but if you can overlook the numerous grammar and spelling errors there are a few genuinely touching moments, brought on by the "what-could-have-been" aspect, and the sharp contrast between the relatively Lighter And Softer Potterverse and the violent, dystopic Narutoverse. However, most of the more exciting conflict seems to center around Itachi and the Narutoverse side of the crossover, and the conflicts on the Potterverse side are solved with relative ease. Most definitely a Fix Fic.

The Boy Who Fell, by Darth Marrs
 * Recommended by User:Looney Toons
 * Crossover with Star Wars.
 * Synopsis: Thirteen years ago, Harry Potter was murdered by Vernon Dursley, and with him went the last hope of magical Britain. Now, as Voldemort and his Death Eaters spread their reign of terror across the Wizarding World, Luna Lovegood makes a wish for someone to come and make it all better. What she gets is Ben Skywalker.
 * Comments: Yes, it really is Star Wars meets Harry Potter. Search your feelings, you know you want to know how this can possibly work.

Vanity, Vice and Voyeurism by MsShayXPear
 * Recommended by: Mac Phisto
 * Crossover with Fight Club.
 * Synopsis: As much as she hates muggles, Bellatrix Lestrange can't help but be fascinated by them. You can learn a lot about a person just by taking a look at how they live. One day, she decides to sneak into the apartment of Ms. Marla Singer.
 * Warning: Rated M, for obvious reasons
 * Comments: Two of the most depraved characters ever, both played by the most beautiful woman in the world... how was I supposed to pass this up??

''[http://www.tthfanfic.org/Story-22035/joshlamont+Fear+Us+We+Are-.htm Fear Us. We Are-] by joshlamont''
 * Crossover with Buffy the Vampire Slayer.
 * Recommended by User:Looney Toons
 * Synopsis: After ending up in the wrong part of the Multiverse, a 27-year-old magic-warping Xander goes to Hogwarts.
 * Comments: Very entertaining. Despite being extremely magically inhibited, Xander adapts to Hogwarts and changes his house, the school, and the whole magical society. Latest two chapters appear to start a crossover with Girl Genius.

Kill Bella by MsShayXPear
 * Recommended by: Mac Phisto
 * Crossover with Kill Bill.
 * Synopsis: Someone has put a hit on Bellatrix Lestrange. And Elle Driver is out for the big fat kill.
 * Warning: Rated M, just to be safe.
 * Comments: A work-in-progress. The sexual tension is intense, but nothing has happened yet. Can't wait for it!

La Blue Wizard, by canoncansodoff
 * Recommended by: Comartemis
 * Crossover with La Blue Girl
 * Synopsis: How do you avoid Oedipus and Age of Consent issues whilst raising a boy whose demonic heritage requires him to feed on sexual energy? If you're Lily Potter, you call on your best friend Emmeline Vance to become a special kind of "wet nurse."
 * Warnings: NC-17. Minor squick warnings for naughty tentacles and a few similarly mild fetishes. No underage sex.
 * Comments: This has got to be one of the weirdest HP fics I’ve ever read that wasn’t explicitly a Crack Fic, not because it’s a lemon and not because it’s a crossover with La Blue Girl of all things but because it can’t seem to decide whether it wants to be a PWP lemon or a (relatively) serious AU fic for the first five chapters or so before it settles on the latter in chapters 5 and 6. Up until that point, the story flip-flops between the Potter family raising Harry (and his two little sisters later on), Lily/James/Emmy’s bedroom exploits, and a few loose nails that throw the story in a totally new direction once Harry grows up and gets to school, like Voldemort accidentally marking  of all people as The Girl Who Lived. Also uses Manipulative!Dumbledore, and Harry's personality is different enough for him to be an OC (albiet an OC who takes very strongly after James), but I recommend it anyway unless you're fatally allergic to lemons.

End of the Line by Shewhogaurds
 * Recommended by Fenro
 * Crossover with Discworld.
 * Synopsis: After death, characters arrive in Kings Cross to board the Hogwarts Express, on it's way to "The Other Place". The only trouble is that the train is always delayed because of the leaves on the line.
 * Comments: A crossover with Discworld, featuring Death, Albert, and The Death of Rats manning Kings Cross, ushering characters into the afterlife, and waiting patiently with those who are waiting to for someone to catch up.

The Girl Who Loved and its sequel, Violence Inherent in the System, by Darth Drafter.
 * Recommended by User:Looney Toons
 * Crossover with Sailor Moon and Ranma ½
 * Pairings: Harry/Usagi, Ranma/Shampoo
 * Status: "The Girl Who Loved" is complete, "Violence Inherent in the System" is complete.
 * Synopsis: Upon receiving some very disturbing news during the summer after his fifth year, Harry does a panicked accidental-magic Apparition straight to China, and falls directly in a Jusenkyo spring... a spring in which one Usagi Tsukino had accidentally drowned the year before. Hilarity Ensues.
 * Warnings: Chapter 9 of Violence Inherent In The System contains mild lemon, and some chapters of The Girl Who Loved have off-screen lesbian encounters which get a fair amount of discussion on-screen. Also, the fic starts out with a mention of m-preg. Fortunately, there is no actual m-preg in the story. In fact, the entire point of mentioning it in the first place was to mock the living hell out of the very idea. Cologne's speech on why the entire concept is idiotic made this troper applaud.

Harry Potter and the Invincible Technomage, by Clell65619
 * Recommended by User:Looney Toons
 * Crossover with the Marvel Universe.
 * Synopsis: A party of executives from Grunnings and their families are given a facilities tour of a factory as part of a joint project with an American firm. When the Dursleys die in an explosion, accidental magic lets Harry be the sole survivor. And when a young child shows visible superpowers on company property, the owner is called in, leading eventually to an 11-year-old Harry Stark attending Hogwarts...

Fictional by Dark Syaoran.
 * Recommended by Shadow AI
 * Crossover with Fate/stay night.
 * Synopsis: Author's Summary: The dictionary defined fiction as thus: something feigned, invented, or imagined; a made-up story. The act of feigning, inventing, or imagining. Yes, Harry thought, this defined him nicely.

Thinking in Little Green Boxes, by DireSquirrel "“Don’t worry, this can’t possibly be as bad as the time he stole Dr. Doom’s credit card and bought everything under the sun.” In Latveria, a certain monarch was looking at his visa bill. “Who dares defile DOCTOR DOOM’S credit score?”"
 * Recommended by Comartemis
 * Crossover with Deadpool.
 * Synopsis: On the night baby Harry was supposed to go to the Dursleys, someone screwed up the addresses and dropped him off at 4 Privy Drive, currently inhabited by one Wade Wilson. Ten years later, Harry gets his Hogwarts letter.


 * Comments: Yes. Harry Potter as raised by the Merc With a Mouth himself. The world will never be sane again.

Culture Shock by Ruskbyte
 * Recommended by: User:Looney Toons
 * Crossover with The Culture.
 * Synopsis: Harry Potter has just received his Hogwarts letter, but really doesn't want to go. After all, who would want to live on a planet of all things? Especially one where the inhabitants still think nuclear energy is an advanced technology. And let's not forget the 42,000-light-year commute.

A Year With Q, by Morena Evensong
 * Recommended by: acg452
 * Crossover with Star Trek: The Next Generation.
 * Author's Description: Q loses a bet with his son. Now he must pretend to be a sixth year student at Hogwarts without using any of his powers. How will Hogwarts react to the new student? Will Q survive the year?
 * Description: The above sums it up rather well. Q goes to Hogwarts for Sixth Year, and his son becomes the DADA teacher. Just... picture that for a moment. Most of the focus is not on Harry, which should come as no surprise to those familiar with the Entity Known as Q. Has a few cameo appearances by the various crews Q has mess- er, that is, a few of Q's friends show up from time to time.

Mutant Storm by Bobmin
 * Recommended by: User:Looney Toons
 * Crossover with the X-Men.
 * Pairings: Harry/Ginny, Scott/Jean, ,
 * Synopsis: After Dumbledore tells him the Prophecy, an angry Harry explodes (figuratively) and discovers he has a strange power, combining intangibility, invisibility and teleportation. Going back to the Dursleys proves to be both a hindrance due to his depression and a chance to practice with his new powers. On the other side of the Atlantic, two powerful telepaths by the name of Charles Xavier and Jean Summers detect the appearance of a very powerful mutant in England... and Charles Xavier realises that he has to come clean on Jean's past.
 * Comments: The first thing the wonderful duo did was to tell readers the fanfic was Harry/Ginny. At first, it explores how Harry reacts to his new powers and how this affects the X-Men as Jean Summers discovers that, adopts Harry and takes him to the X-Mansion. It then goes forward from that, passing over things such as the revelation of his mutant powers to the Order of the Phoenix, his going back to Hogwarts and how Voldemort plans to include the mutant community in the British Magical War. It includes a believable Manipulative!Dumbledore, Snape working more for Voldemort than Dumbledore (not on his own volition), a great (and funny) Wolverine, and, finally, a good development of a relationship between Harry and Ginny.
 * User:Looney Toons: Seconded. It's not great literature and we get a fair amount of Ron-bashing, which is a typical feature of Bobmin's work, but it's still a fun read.

Harry Potter and the One Ring of Power by Technomad
 * Crossover with The Lord of the Rings.
 * Recommended by Eoppen
 * Synopsis: Voldemort tried to obtain the One Ring, but it was intercepted. Now, the Boy who Lived must take over the quest to Mordor, with Hermione Granger, Ron Weasley, and...Draco Malfoy?...as his companions.
 * Comments: This may be the first full-length Lord of the Rings/Harry Potter crossover. The author gives us sections from the POVs of Harry himself, Ron, and Hermione. There are also nods to other writers, such as Lois McMaster Bujold, scattered through the text.

The Denarian Renegade, its sequels The Denarian Knight, The Denarian Lord, The Denarian Variation, and the extras The Denarian Omakes by Shezza88
 * Crossover with The Dresden Files.
 * Recommended by Jinx, User:Looney Toons
 * Synopsis: A seven-year-old Harry finds a blackened silver coin at a low moment in his life.
 * Comments: Harry is delightfully snarky and beautifully balanced between good and evil. It also has the best written Dumbledore I've ever read.
 * Seconded by User:Looney Toons: And don't miss its sequels The Denarian Knight and The Denarian Lord, and the extras The Denarian Omakes.
 * Harry becomes an insufferable Jerkass Mary Sue within the first three chapters, and remains such throughout the next thirty. Despite excellent plotting, quality writing, and an amazingly well-characterized Dumbledore.

Alexander Harris and the Shadow Council by Tenhawk
 * Recommended by User:Looney Toons
 * Crossover with The Addams Family and Buffy the Vampire Slayer.
 * Synopsis: So far this is a threeway crossover between The Addams Family, Buffy the Vampire Slayer, and Harry Potter. The main focus is on Xander Harris and Wednesday Addams as they they go to Hogwarts but Hermione from the "Golden Trio" does get her share of the story. The story starts of with a slight retelling of the first Harry Potter book and unravels it as Xander works his particular brand of chaos. This could well be described as a day-in-the-life story.
 * "Comments": Highly recommend this story. Xander gets adopted (sort of) by the Addams Family. Wednesday terrifies everyone at Hogwarts. Buffy hasn't shown up yet.

Harry Potter and the God of Death by Nesarna
 * Recommended by PeppermintWinds
 * Crossover with Bleach
 * Status: Ongoing
 * Synopsis: Getting recruited for another war wasn't quite what he had in mind when his father announced a family trip to England. But now that he's here, Kurosaki Ichigo finds himself pulled into a web of deception, government lies, and centuries-old conspiracies...

The Hero by GreyFitti
 * Crossover with Fullmetal Alchemist.
 * Recommended by RoamingShadow
 * Synopsis: Takes place during Harry Potter Chamber of Secrets]] for Harry Potter and post Conqueror of Shamballa for Fullmetal Alchemist. When Ed and Al went back to close the gate to their world, the gate drops Ed into Hogwarts. There, he starts working as the Alchemy Professor to find a way home. But, the trio becomes suspicious of Ed...
 * Pairing(s): None.
 * Comments: Complete. This story is well-written and a good read. Though, Edward does speak with a German accent and the story is mostly seen in his third person point of view. I find this crossover very interesting, from beginning to end, it thrilled me.

Percy Weasley: Vampire Hunter by Viola
 * Recommended by Those Dancing Days
 * Crossover with Angel.
 * Synopsis: In the summer after Order of the Phoenix, Percy Weasley is is a man without a mission. Recently sacked form his Ministry job after the firing of Fudge, Weasley sets off to find another job. His job hunting takes an unexpected turn when he encounters a vampire, and helps Kingsley Shacklebolt with several missions. With the help of Lorne, Ginny, and Mrs. Longbottom, Percy sets up an "Auror-for-hire" office, hoping to be a "Champion for the Good of Mankind".
 * Comments: Incomplete. This story is well worth the read, even though the updates are sporadic (luckily, there's a tag for the story on the author's LJ). Everyone is still in character, plus there's a likable Ginny Weasley!

12 Moves Sideways by Silver Pard
 * Recommended by Aimsme
 * Crossover with Death Note.
 * Synopsis: After the Yotsuba Arc, Light becomes the new Defence Against the Dark Arts teacher. Harry decides he needs watching.
 * Comments: Despite being short compared to most of the others on this list, 12 Moves Sideways packs a powerful punch. It's beautiful, almost wistful, with hints of something darker- it might just be because this Troper is a Light fan, but her heart broke at the Erised scene.

To Face the Wolf by Maglor's_finch
 * Recommended by Goodwrench
 * Crossover with The Silmarillion.
 * Synopsis: In the Hogwarts dungeons, Snape finds a mysterious, badly wounded stranger. He appears to have been bitten by a werewolf. What happened?
 * Comments: Absolutely fantastic crossover with Tolkien's Silmarillion. This one's a tearjerker.

Double Trouble by kellemarine
 * Recommended by Pumpkin Lore
 * Crossover with The Nightmare Before Christmas.
 * Synopsis: Everyone knows what happened when Sirius fell through the veil. What if something different happened to Harry? Harry ends up in Halloweentown where he meets Jack Skellington. Things change forever for Harry and Jack and nothing will ever be the same. Set 7½ years after the Christmas fiasco and immediately after the Ministry battle in Harry Potter and The Order of The Phoenix.
 * Comments: I have to say, I was not expecting this to be any good (as much as I love crossovers, sadly most Fanfic crossovers are lacking). While some things seem to be Hand Waves or possibly even complete Ass Pulls, depending on how you look at it, the story is quite good, and everything makes sense if you can take some Acceptable Breaks From Canon (like Harry and, according to the author notes, Sirius surviving the fall through the veil). The fic has yet to be completed. *goes to bug the author to write more already review the fic*

Duality, Beneath Between Beyond by AvacadoLove
 * Recommended by Blue Hospitality
 * Crossover with Avatar: The Last Airbender.
 * Synopsis: An accident with two linked vanishing cabinets transports Prince Zuko and Draco Malfoy into a place between their two worlds. To escape they need to learn to work together, and it may turn out that the two aren't very different after all...

Damned Demented Demons, Vile Violent Vacations by hell_half_acre
 * Recommended by bettername2come
 * Crossover with Supernatural.
 * Synospsis: Damned Demented Demons Harry saves the Winchesters from a Dementor attack, but the Winchesters aren't the only ones that need protecting. Takes place during Season 4 of Supernatural and Post-DH for Harry Potter. Vile Violent Vacations is a sequel that takes place during the middle of season 5 of Supernatural.
 * Comments: The author does a great job of combining the two universes, as well as giving some good insights into what the Harry Potter characters are up to currently. Sticks surprisingly close to Canon.

The Best Defense, A Good Offense, and a few sidefics by JoIsBishMyoga.
 * Recommended by Crown Clown
 * Crossover with Yu Yu Hakusho.
 * Pairing(s): The romance is mostly in the background, but Hiei/Kurama and Ron/Hermione (male slash and het).
 * Synopsis: Voldemort's return has caught the attention of more than the Order of the Phoenix. The Spirit World's best are on the case, but can they handle Hogwarts (or Harry) without blowing their cover?
 * Comments: One of the best (and longest running) Harry Potter crossover fics out there. Well-written and better plotted, with fun insights into it's view-point characters, this series is one of the crowning jewels of crossover Fanfic.

Harry Potter and the Borg by LocutusLupin
 * Recommended by The Rich Sheik
 * Crossover with Star Trek: The Next Generation and.
 * Synopsis: It was supposed to be Harry's day off. No such luck for the man that defeated Voldemort 13 years ago. The Borg invade and its up to Harry to save the world, again. But can Real Magic defeat Magic From Technology?
 * Comments: Starts off as a basic crossover, but throws a curveball at you when its revealed that  A recurring theme here is that nothing is as it seems, and It Got Worse. And Worse. And Worse.

Draco Malfoy and the Snarky Pen Pal by shadowglove
 * Recommended by The Rich Sheik
 * Crossover with Smallville.
 * Synopsis: Mandatory Muggle Studies class requires Draco to write to a muggle pen pal, who happens to be Chloe Sullivan. And there was much snarking.
 * Comments: A short fic, but with plenty of Character Development for Draco and his attitude towards muggles. Ends abruptly but the author is planning a sequel, which will be added if/when it is written.

Tactical Espionage Action Metal Gear Solid Slytherin Eater by Rogue 11
 * Recommended by jakesolong
 * Crossover with Metal Gear.
 * Synopsis: What if Harry Potter got trained by Solid snake at a young age and learns to fight mages and monsters the way Big Boss does. Guns are included. 'If I ever take over the world I'm making a law against that kind of bubbly happiness...' The man with the eye patch thought.
 * Comments This one is an awesome oddball that's funny, well written and worth a read.
 * It is a really good story, well written and funny at many times. Unfortunately, it is a Dead Fic.

Harry Potter and Ascension of Ra by Apocalypse Thou
 * Recommended by Magyareagle
 * Crossover with Smallville.
 * Synopsis: Voldemort has been vanquished from power and Harry from Britain. Aiming to start a new life in muggle America Harry moves to what he thinks is a small quiet town to start over. His destiny has just begun. Smallville Xover. Harry Potter/Lois Lane. Begins Season 4
 * Comments: Easily one of the best and most realistic crossovers I have ever seen, this one seamlessly blends a postwar, somewhat troubled Harry with Smallville canon. The writing style is excellent, and better yet, it manages to avoid most of the common pitfalls of the genre.
 * Caution: Early chapters have Harry on the edge of God Mode Sue status, but that gets toned down over time. Also Harry and Clark rarely do any superheroing together, which is kind of disappointing.

The Dead of Winter by ForeverFalling86
 * Recommended by fullmetalpianist
 * Crossover with Bleach.
 * Status: Complete
 * Synopsis: Hitsugaya Toshiro is sent to Hogwarts to investigate the presence of Dementors and protect living souls from them. Takes place in Harry's third year at Hogwarts.

Trial By Fire by celticbard
 * Recommended by Kae Marshall
 * Crossover with Silent Hill.
 * Synopsis: Draco lifted his head, blinking the blood away from his eyes. Pain seized him, throwing him against the driver’s seat with all the force of the Cruciatus Curse. Mocking shards of memory danced through his dazed mind.The sirens. The cop. The slick road. His car was nestled against a guardrail, the remnants of his shattered headlights dusting the blacktop like frost. And outside, the sky wept soot.
 * Comments: Well written and in character. You don't even have to watch the Silent Hill movie to enjoy the fic.

Water Aerobics for the Aquaphobic by Minnionette
 * Recommended by RealityPhobia
 * Crossover with Ranma ½.
 * Synopsis: In retrospect, Harry should've known that Umbridge's field trip to the ancient springs of Jusenkyo was an unmitigated disaster waiting to happen. Having fallen into the Springs of the Drowned Emo and Drowned Emu, Harry supposes he's luckier than, say, Snape (Spring of the Drowned Unicorn) or Ginny (Springs of the Drowned Pig and Homing Pigeon), but there are more problems in the upcoming year than just curses that have no known cure: Voldemort takes advantage of his own cursed form to infiltrate Hogwarts as Luna's new pet bunny and actively plots the demise of, well, everyone. And there's really no way to explain Lucius Malfoy, the benevolent Buddhist monk. (AU Harry Potter and The Order of The Phoenix; Ranma ½ crossover) Features many minor characters with personalities –- especially Daphne Greengrass and Blaise Zabini.

Harry Potter and the Colour of Magic by Chardvignon.
 * Crossover with Discworld.
 * Recommended by MrMous
 * Synopsis: This fanfic posits a post-Voldemort universe in which Harry Potter has survived, and succeeded in his ambition to become an Auror. After a raid which backfires spectacularly, Senior Auror Kingsley Shacklebolt needs to have Harry re-trained to think like a copper. The only person he can trust? Commander Sir Samuel Vimes, Ankh-Morpork City Watch. Only, magic is a lot more powerful in the Discworld, so Potter had better be careful where he points that thing...
 * Pairing(s): Harry/Hermione, Ron is mentioned as being happily married to Luna.

Hellblazer: Hogwarts by Camwyn.
 * Crossover with Hellblazer.
 * Recommended by User:Looney Toons
 * Synopsis: After interferring in a magical fight (armed with a half-brick in a sock), John Constantine finds himself in another world; a world where magic works differently, demons can't be summoned up, and children go to a magical school called Hogwarts. Luckily, he manages to strike a bargain with Albus Dumbledore, who has the following offer: He'll do everything in his power to help Constantine get back to his own world, if Constantine in the meantime takes the job as Defense against the Dark Arts teacher at Hogwarts.
 * Comments: The story was written before Half-Blood Prince, and unfortunately, seems to be a Dead Fic... but the ten chapters that are up are really well done, with many clashes between Constantine and the HP world. Harry himself doesn't show up until chapter ten, but Constantine's attempts at figuring out Hogwarts and his interactions with the Hogwarts staff (and ghosts!) are thoroughly entertaining. Possibly the highlight of the story is the friendship that grows between Hagrid and Constantine—and Camwyn even gets Hagrid's accent right, a rarity in fanfic.

The End of the Beginning by Mariner.
 * Crossover with Buffy the Vampire Slayer.
 * Recommended by Kurukami
 * Synopsis: London, 1981. The Dark Lord's reign of terror is at its height, and two Muggles possessed of their own magic, entirely different from that taught in the wizarding world, are about to stumble into the war. Two Muggles named Rupert Giles and Ethan Rayne...
 * Comments: Written a little before the release of Harry Potter and The Order of The Phoenix, Mariner puts forth an plausible alternate history and an entirely believable reason why Lily's sacrifice saved her son. Aside from the how, and the introduction of Buffy-verse magical capabilities, doesn't really depart from the establish canon within the books as released to that point—the fic eloquently provides another history as to how the Potterverse could have gotten to where it is now.

Harry Potter and the Secret Link by Capricious Purple Clarity
 * Crossover with Mobile Suit Gundam Wing.
 * Recommended by QuatreWinner
 * Synopsis: Watch as Duo chips away at the very foundation of Hogwarts as he breaks down House walls, befriends Gryffs and Slyths alike, mugglfies Malfoys, and flushes cherry bombs down school toilets.
 * Comments: This fic is simply too much to adequately summarize without spoiling anything. Duo is completely in-character throughout this whole thing, and it's his character that "mugglefies Malfoys" et al. An alternate summary is "Duo Maxwell's unique brand of luck strikes again. Ron wants to keep him, even if he does have some weird obsession with flirting with Snape. Snape just wants to know where to bury the body." It's just... everyone's in character. The plot makes sense. I'm not really doing it justice, really. Just read it and see what I mean. It also has a sequel, Harry Potter and the Forgotten Heirs.
 * Warnings: Slash! There is the aforementioned Duo/Snape flirting, as well as 1x2, 3x4, and Harry/Draco.

The Savior and the Scourge by Random Dispatcher
 * Crossover with Buffy the Vampire Slayer.
 * Recommended by: force42
 * Synopsis: Spike comes to Hogwarts to protect the Malfoy heir. He becomes fascinated with the angsty Harry Potter and the wonderful scent the teen exudes. What happens when the Scourge of Europe knocks up the Savior of the Wizarding World? COMPLETE!
 * Comments: This is a fic you can read again and again and laugh ever time. At 20 chapters, it's on the long side, and there are a few spots that drag, but overall, it is worth reading.
 * Warnings: Slash and mpreg (Harry/Spike)

Harveste and the rest of the Harveste series by kyaru-chan
 * Crossover with The Addams Family.
 * Recommended by: User:Looney Toons
 * Synopsis: He's done it. He's just five years old, but he's finally done it. The Dursleys are gone. And now he's with a new family who seems just as twisted as he is. How strange.
 * Comments: Dark, twisted, macabre, and glorious. After killing the Dursleys, Harry is adopted by the Addams family and takes the name Harveste. It's a very different Harry who goes to Hogwarts. The series is still being written, and is currently in its sixth installment.
 * Update, September 2014: Despite its very promising start, after several installments this series began to show serious decay in focus and quality, and by late 2011 the author had more or less abandoned writing alltogether (at least under this name on Fanfiction.net).  The series as a whole is now dead.
 * Warnings: Blood, gore, death, torture, cross-dressing

We Are Nothing by Ruskbyte
 * Crossover with A Nightmare on Elm Street.
 * Recommended by: User:Looney Toons
 * Synopsis: Snape's Occlumency lessons have shattered the last defences of Harry's mind. Now, completely unprotected, his dreams have become home to a nightmare other than Voldemort. A nightmare that has taken on a life of its own.
 * Pairing(s): Ginny and a minor Ravenclaw character named Michael Corner.
 * Warnings: Very gory, strong language, and some racial and sexist epithets (all of them by Freddy).
 * Comments: Appears to have become a Dead Fic.

Visited by a Doctor by Tangerine-Alert
 * Crossover with Doctor Who.
 * Recommended by: OliverSmillie
 * Synopsis: Harry is visited by the Doctor throughout his seven years at Hogwarts, then moving through Harry's life outside school. As Harry takes on both Voldemort and Aliens.
 * Pairing(s) : Harry/Daphne in the later chapters. Harry/Ginny for a tiny bit.
 *  Warnings: starts out much like the books but with The Doctor appearing here and there. Turns into an AU Story latter on, as the story references both Harry Potter events and Doctor Who'' events.

Loss by BiJand
 * Crossover with Doctor Who.
 * Recommended by: IraTheSquire
 * Synopsis: Still affected by the losses of previous years, and by the destined, upcoming death of Dumbledore, the time travellers are again in Hogwarts, a castle victim to a creature which has suffered losses of its own
 * Comments: This is actually the sixth part of a series. Basically think the original Harry Potter timeline being screwed over by events and the 11th Doctor, Amy and Rory trying to fix it. Extremely impressive in the way that it pulls no punches, with Anyone Can Die Turned Up to Eleven, with the implications explored. Possibly the best HP/DW crossover that takes into account that Harry Potter is fiction in the Whoverse.

Wizards Abroad by fourth rose
 * Crossover with Discworld.
 * Recommended by: DrWillHatch45
 * Synopsis: When Dumbledore sends him to the "perfect hide-out", Draco doesn't know yet that he'll soon wish Voldemort had got to him first...
 * Basically, Draco hides out at Unseen University on the Disc while Voldemort is out looking for him.

Old Country by astolat
 * Crossover with Supernatural
 * Pairings: Sam/Dean
 * Recommended by: Meteor
 * Synopsis: Dean Winchester is a Hufflepuff who thinks he's a Gryffindor, and Sam Winchester is a Slytherin who thinks he's a Ravenclaw. Discuss. (Dean and Sam must attend Hogwarts to obtain a magical inheritance. Story occurs the year after the Battle of Hogwarts.)

The Most Deadly Alliance by Emachinescat
 * Crossover with Merlin.
 * Recommended by LordFedora
 * Synopsis: A deadly alliance has been made, a terrible deal has been struck. When Harry and his friends find themselves in ancient Camelot, they and their new friend Merlin are faced with a terrible evil that is intent on killing them all.

The Magic of Torchwood by Bella the Strange
 * Crossover with Torchwood.
 * Recommended by User:Looney Toons
 * Synopsis: The Torchwood team have been accepted at Hogwarts School of Witchcraft and Wizardry. Set between "Adam" and "Reset". Rated T because of Jack Harkness, swearing, mature themes, slash etc... it's Torchwood!
 * Comments: An amazing piece of work that age-regresses the Torchwood team and sends them to Hogwarts at the beginning of Harry's third year. Story takes place from there onwards and masterfully inserts Torchwood during the years and develops pre-existing minor characters as well as introducing rounded ones.

Death's Visage by Black-Raven3
 * Crossover with Hellsing.
 * Recommended by Navllyk
 * Synopsis: After Harry's 5th birthday, his true powers are unleashed, powers so dark that Dumbledore felt the need to bind them. Fleeing the Dursleys just before his 11th birthday, he seeks refuge with his family's ancestral allies, the Hellsings. DARK.
 * Comments: Contains Ron bashing, Depressed!Harry and !Harry, but has, thankfully, avoided Draco in Leather Pants so far.

Special Men by sineala
 * Recommended by: Ainyre
 * Crossover with The Professionals
 * Synopsis: It is 1975, the height of the First Wizarding War, and Voldemort's reign of terror has spread far and wide. His followers, the Death Eaters, have begun cursing and killing Muggles. As CI5's brief includes domestic terrorism, the responsibility for stopping Voldemort falls on them—but this is not a fight they can win without magic. For this reason, Ray Doyle, an Auror, is transferred from the Ministry of Magic to join CI5, as its first and only wizard. But his abilities must remain secret from his fellow agents, including Bodie, his new partner. But Bodie seems to have a few secrets of his own, and it especially doesn't help that Bodie is so damned attractive...
 * Pairing: Bodie/Doyle
 * Tags: Slash, Fusion Fic

Mystery Science Theater 1000 by Hardman5509
 * Recommended by Hardman5509 (Currently desperate to hear anything.)
 * Fandoms: Shadow Hearts Mystery Science Theater 3000 My Immortal
 * Synopsis: In the style of Mystery Science Theater 3000, the main characters from the Shadow Hearts series, Yuri Hyuga, Alice Elliot, Johnny Garland, and Shania are forced to watch/read horrible Fan Fics by Proffesor Gilbert and Nicolai. From the 11th chapter on, they tackle My Immortal, The Manos of the Internet. Currently covers the first seven chapters.

Ace of Spades by LeontinaStardust
 * Recommended by: feral
 * Crossover with Batman.
 * Pairings: The Joker/Harry Potter, Poison Ivy/Harley Quinn
 * Synopsis: Slash Fic Featuring Insane!Harry. Betrayed by his friends and seemingly stripped of his powers Harry Potter ends up in Arkham Asylum which does nothing to help his problems. There he meets a fascinating man with scars on his face who would also like to see the world burn... Loosely based in the Nolan-verse Batman film series, this Joker is an amalgamation of the Heath Ledger and Jack Nicholson versions. Now with a Tropes page.

The Butterfly Effect by Philo Vance
 * Crossover with Sherlock Holmes.
 * Recommended by Logatel
 * Synopsis: What if, instead of Ron Weasley, Harry Potter met someone else while going to Hogwarts? Would that little detail change just a little detail or would it change everything?
 * Comments: The story replaces Ron Weasley (who simply does not exist within the story's context) and replaces him with an eleven-year-old Sherlock Holmes. It's surprisingly well-done in that it doesn't have Sherlock simply obliterate the series plot and that it doesn't turn into rather frequent logic abuses that some stories take, instead opting to preserve the series' overall atmosphere while changing its pace. It's definitely worth a look if you like both fandoms.

Savior by JoeHundredaire
 * Crossover with Buffy the Vampire Slayer.
 * Recommended by User:Looney Toons
 * Synopsis: "She's Luke Skywalker. She's here to rescue him." Illyria goes to Hogwarts and chaos ensues.
 * Comments: Very funny, especially the Luna/Illyria interactions. Hints of F/F and poly shipping, but nothing actually explicit.
 * JoeHundredaire deleted all his stories from TTH some years ago, and only a fragment of this particular one remains on the Wayback Machine.

Whispers in Corners by esama
 * Recommended by darknesshiddeninlight
 * Crossover with Sherlock.
 * Synopsis: Everything started with a stumble—his new life in a new world as well as his surprisingly successful career as a medium. Harry/Mycroft eventual slash. Takes place after "The Great Game" and after a AUish ending of the Harry Potter books.

In which Snape befriends an old grey donkey, and life is gloomy, as usual by gm_weasley
 * Crossover with Winnie the Pooh.
 * Recommended by: Ladysugarquill
 * Synopsis: Snape Apparates wrongly, meets Eeyore. They commiserate. It's hilarious.

The Ninja Wizards saga by ladylisse
 * Crossover with Naruto.
 * Recommended by: Ladysugarquill
 * Synopsis: Two one-shots ( Three Good Reasons and Home Front ) and eight ficlets (so far), putting the Harry Potter world inside the Natutoverse. It doesn't have any real plot besides worldbiulding and character study, but it is absolutely fantastic. Snapshots of three young shinobi. In another time and place, this would be magic.
 * Tags: Contains spoilers for Harry Potter up to HBP, and some for Naruto.

Not Quite a Maia by Kara's Aunty
 * Crossover with The Lord of the Rings.
 * Recommended by: BlackWingedAlchemist
 * Synopsis: "Middle Earth has a problem: Gandalf the Grey is AWOL in Time & Space after destroying the Balrog of Khazad-dûm. But who will take his place in the Quest to defeat the Dark Lord Sauron? Not who you think... HP/LOTR Crossover. Wildly AU!" Molly Weasley, Neville Longbottom, and another mysterious visitor travel to Middle Earth. Hilarity Ensues.
 * Comments: Seriously, this is the best HP/LOTR crossover this troper has ever read. Though there is little of the titular character, except for mentions, Neville and Molly are absolutely brilliant, and and "Archibald" are side-splittingly hilarious. At a current 36 chapters and 427k+, it's nothing to sneeze at, either.

Shifting Times by Shadewolf7
 * Crossover with Animorphs
 * Recommended by The Warrior of Many Faces
 * Synopsis: The Animorphs had an unofficial seventh member. A very young girl who got caught up in their secret war and was given morphing powers to survive. That girl moved to England. And years later, an owl comes for her.
 * Comments: Brilliant. Simply brilliant. Her morphing abilities have well-planned effects on her magic, the story is well-written, and the characters feel real. Main character is an author insert, but it seems to be handled well; Your Mileage May Vary, though, as a few reviewers have noticed some Sue-ish qualities. So far, the main HP characters haven't shown up in earnest; if you don't like OC wizards, don't read this. The fic appears to have died, however.

The Wizard in the Shadows by Nimbus Llewelyn
 * Recommended by The Enmity Of Ages 1994
 * Crossover with The Lord of the Rings
 * Synopsis: After the Second Wizarding War, Harry goes to rest and recuperate in Middle Earth, 4 years before the War of the Ring. Pity no one told him about the resident Dark Lord. 4 years on Harry goes with the Fellowship, with the chief objective of distracting and fighting Saruman. But when did any of Harry's plans not fall apart?
 * Comments: This fic yo-yo's between genres, and after the first chapter (short and mostly to get to Rivendell quickly), it gets longer and better. The Rohirrim gets A Day in the Limelight with numerous sections about what is happening in Rohan, giving us an interesting and well written Theodred. Harry is powerful, having taken a further level or 3 in badass, and enjoys Playing with Fire, and cracks jokes every now and then, but is far from invincible, getting his arse handed to him on several occasions and remains vulnerable both emotionally and physically. The narrating owes more than a little to the Discworld and The Hitchhiker's Guide to the Galaxy in tone, but blended with gentle handling off the quieter scenes. While far from perfect, it is readable, funny and spectacular. Another bonus is the impressive update rate.
 * Now has a prequel, The First Meeting of Aragorn and Harry with the promise of more and an eventual expanded universe.
 * Pairings: Word of God says that Canon is being adhered to as regards pairings.

The Demon Who Lived by Kolarthecool
 * Recommended by feral
 * Crossover with Naruto
 * Synopsis: AU, The Potter family are descendents of Uzumaki Naruto and Harry was only "The Boy Who Lived" because the Juubi, a powerful demon, gave him a portion of his powers, making him a true demon and creature of darkness. With the combined knowledge of his ninja forebears, Demon!Harry's mischief turns Hogwarts upside down as he curbstomps his enemies into submission.
 * Tags: Crossover, demons, Dark Is Not Evil, Het, Marty Stu, God Mode Sue, Jerk Sue, Villain Sue, Mary Tzu, Dark!demon!ridiculously_overpowered!ninja!Harry, Evil Is Cool, Rule of Cool, Curb Stomp Battle, Badass, Kick the Son of a Bitch

Herwald von Einzbern and the Philosophers Stone, by kyugan
 * Recommended by Xamusel
 * Fandoms: Fate/stay night, Harry Potter
 * Synopsis: As from the Fanfiction.net entry: "The 5th Heaven's Feel has been averted, with no apparent victor, but for Herwald von Einzbern, recently turned eleven, a whole new adventure is about to begin in a world he left behind ten years prior."
 * Comments: A story that starts off a series by kyugan,  The story is complete, but it has a sequel up set during the events of The Chamber of Secrets, which shows that the author knows what he's talking about....

Professor Takamachi by Rick Dias
 * Crossover with Magical Girl Lyrical Nanoha.
 * Recommended by EpicFightingTroper
 * Synopsis: Dumbledore tries to find a new Defense Professor, he gets a certain White Devil.
 * Comments: A very fun read, which mostly consists of Nanoha scaring the crap out of everyone, all the students getting more badass through superior training techniques and Umbridge getting her just desserts at the end. Also, Harry . If you think that sounds like a good time (or you're a fan of Harry Potter and/or Nanoha), than there is no excuse for not checking this out.
 * YMMV. The quality of the writing is far from good.

Happiness is a Broken Wand by Embracing Madness
 * Crossover with The Lord of the Rings
 * Recommended by: Fenro
 * Synopsis: Severus Snape just wants a new, peaceful life in Middle-Earth, but with a vicious war arising and a new Dark Lord gunning for him, he'll have to fight to get that wish. Magic and battles, familiars and friends. Slytherinesque cunning shall always prevail. This story takes place near the end of DH. Gen Fic.

A Study In Magic by Vixit
 * Crossover with Sherlock Holmes
 * Recommended by: Lustheron
 * Synopsis: When Albus Dumbledore shows up at Baker Street with strange demands and baby-filled picnic baskets, Sherlock Holmes is less than thrilled. Featuring Detective!Harry, Competent!Quirrell, and the world's only private consulting detective.
 * Comments: A very interesting take on Harry raised by Sherlock Holmes. Harry isn't all-knowing or perfect. Holmes is just as antisocial and distant as canon. And Quirrel is both not evil and incredibly epic.

Uchiha Potter By Choska Kurenai
 * Crossover with Naruto
 * Recommended by: autopanda
 * Synopsis: After Voldemort's fall, Harry was raised as an Uchiha with his cousins Sasuke and Itachi, unaware of his other heritage. How will Hogwarts deal with this kunai-weilding, Ass-kicking Uchiha Harry Potter? -Beta revision ongoing-
 * Comments: A very well written story where Harry is raised by the Uchiha and has all the problems of the massacre, except he shares them with Sasuke.

Penance by Laora
 * Crossover with Fullmetal Alchemist
 * Recommended by: Purple Queen 15
 * Synopsis: During the Promised Day, Ed and Al end up pulled through the Gate and into the Wizarding World, shortly before the events of Order of the Phoenix. Conflicts between magic and alchemical science arise as Ed and Al try to figure out how to get home, Harry and friends take on the war against Voldemort, and all must face an even greater evil than they can imagine. Story is complete.
 * Comments: A very well-written crossover, characterization stays close to canon and has a great plot. Spoilers for anything past manga chapter 105 or Order of the Phoenix.

''[http://www.fanfiction.net/s/3054928/1/YAHF_Well_Something_Like_That YAHF? Well Something Like That]'' by wargear
 * Crossover with Buffy the Vampire Slayer
 * Recommended by: User:Looney Toons
 * Synopsis: When the Scoobies wake up in Hogsmeade with no idea how they got there, wearing other people's faces, and with some of their dead apparently resurrected, they're pretty sure something strange is going on. It is Halloween, after all. But this time it's not Ethan Rayne who's behind things...
 * Comments: The first, and maybe only, time you will see the classic Buffy "Yet Another Halloween Fic" plot turned on its head and played from the other side. I'd say more, but it's too easy to spoil the fun.

Of Slings and Arrows by the original Pe
 * Crossover with X-Men: Evolution
 * Recommended by: Omeganian
 * Synopsis: Harry is sent to Azkaban for murdering his relatives. After some time, Professor Xavier pulls him out. Later, Dumbledore wants the mutants to help him, so they go into Hogwarts - and Harry is without disguise.
 * Comments: Old and good. Not too cliche.

Mina Aino: Witch in Training by hersheyman
 * Crossover with Sailor Moon
 * Recommended by uncannybeetle
 * Status: Complete, with two sequels
 * Synopsis: Minako, aka Sailor Venus, is a third year at Hogwarts, and in Hufflepuff House (that's different). An encounter with the dementors stirs memories of a past life. She must balance investigations into her past with schoolwork, Quidditch, and the looming threat of Sirius Black Minako/Harry in the sequels
 * Comments: One of the best flowing crossover stories out there. Events follow naturally. Also a good way to see the story of Harry Potter from an outsider's point of view.

Harry Potter and the Return of the True Sorcerers by Magicalfoci
 * Crossover with Cardcaptor Sakura
 * Recommended by Athenaswings
 * Statis: On hiatus. The author updates every two or three years sometimes.
 * Synopsis: There is a strange rift that separates them, and when they start down the path to seek the answers, they find that it requires them to take on a duty that will utterly change their lives for the wizards... and the sorcerers.
 * Comments: With all the Harry Potter and Cardcaptor Sakura fics out there a certain fanfic has to stand out. This is that fanfic. The world building is absolutely amazing. Does it sound cliched? Yes. Is it well written? Absolutely. The author gives sporadic updates but its still worth a read. And yes a Harry Potter crossover with Card Captor Sakura can be done. This proves it.

Harry Potter and the Wrath of Jashin by MegaKiraraLover
 * Crossover with Naruto
 * Recommended by phoenixyfriend
 * Synopsis: And after his defeat, Hidan is confident Jashin will come rescue him and make the world a better place...too bad no one would have believed him if he were to tell. More importantly, too bad he's right! Not!Romance!Centered Super!Godlike!Harry!is!Jashin

Harry Potter and the Ultimate Force and its sequel, Harry Potter and the Circle of Light by DarkKing666
 * Recommended by Jonathan SCE
 * Crossover with Ah! My Goddess
 * Synopsis: When an alarm go off in the Prophecies section of Heaven warning that a prophecy has gone astray, it is up to the three goddesses, and Keiichi, to fix it. Starting with them all moving to England and adopting a certain 8-year-old boy...
 * Has a manipulative Dumbledore trying to get Harry back.
 * The first story is set in 1989, two years before Harry goes to Hogwarts; the second begins his school career. The canon of Ah! My Goddess is current to chapter 278, published in the fall of 2011.

The Golem of New Jersey by PhinFerbSentai
 * Recommended by Maniago
 * Crossover with Megas XLR
 * Synopsis: Alecto Carrow, the last fugitive death eater, discovers Lord Voldemort's will that contains details of his plan to resurrect a legendary monster named The Golem. She goes to New Jersey to find this creature and use it to avenge her master. Harry and Ron, now both Aurors, are given the assignment to stop her. But when the Golem is awakened, they are forced to work together with Coop and Megas to fight it. And to make matters worse, the Glorft also notice the Golem and plan to make him their ultimate weapon.
 * Set in 2004, six years after Deathly Hallows and during the first season fo Megas XLR.

Nanoha Takamachi and the School of Witchcraft by Ryvaken Lucius Tadrya
 * Recommended by Looney Toons
 * Crossover with Magical Girl Lyrical Nanoha
 * Synopsis: When men with sticks and strange magic attack retired TSAB Admiral Graham in England, the TSAB discovers that Earth has a native magical population that is both well-organized and well-hidden.  As part of a diplomatic outreach program between the TSAB and the Wizarding World, Nanoha Takamachi and Fate Harlaown are dispatched to Hogwarts School of Witchcraft and Wizardry—and the Wizarding World may never be the same again.
 * Comments: Fun, well-written crossover.  Incomplete, but not a Dead Fic.

Meadows of Heaven by Mystical Magician
 * Recommended by Looney Toons
 * Crossover with: The Chronicles of Narnia
 * Status: Complete
 * Synopsis: When Susan Minerva Pevensie finds herself alone after the deaths of her siblings, she discovers that she possesses another kind of magic besides that of Narnia, a magic that leads her to the British Wizarding World, marriage, a teaching career—and a destiny at the side of a prized student.

Harry Potter and the Elder Sect by Clell65619
 * Recommended by Looney Toons
 * Crossover with: Bewitched
 * Status: Complete
 * Synopsis: When Voldemort attacks the Potters in 1981, he attracts the attention of Harry's many-times-great-grandmother, Rowena Ravenclaw—or as she is better known in 20th-century Connecticut, Aunt Clara.  She casually obliterates the Dark Lord, and when she finds young Harry possesses both wizard and warlock magic, takes him to be raised by his distant cousin and her husband, Samantha and Darren Stevens.  However, when Dumbledore discovers that Harry is being raised by and as one of the near-divinely-powerful Elder Sect, he refuses to let something as trivial as common sense and self-preservation stand in the way of his need to control every aspect of the boy's life...
 * Comments: Delightfully funny story, deriving a lot of humor out of the vast disparity in power and flexibility between Bewitched ' s magic and that of Harry Potter's Wizarding World.  Only six chapters long, because the author realized that this very disparity also made it hard for anyone from Harry Potter to be a credible threat; so he wrapped up the story before it became tiresome.  Recommended.