The Titans' Orb is a magical stone created by the Titans of Harmony to protect Equestria from otherworldly threats. After a vengeful demigod breaks loose from Tartarus, the Orb is shattered into six pieces and sent to Planet Earth, scattering across the globe. Twilight and her friends are sent to retrieve it at once, for all of Equus is now in grave danger.

Meanwhile on Earth, there lives a boy named Callum, recently fatherless and enduring the torment of an abusive family. He is soon to discover that the fictional characters from his beloved T.V show, are not so fictional.

Alongside his newfound companions, he is soon to embark upon a great adventure.

To find the Titans' Orb...

While exploring a dungeon with her long-lost sister a mysterious event causes a Death Knight of the Ebon Blade to arrive inside the Everfree Forest on Equestria. With her normal means to return home out of commission, she searches the forest for any signs of civilization encountering hostile wildlife until she arrives at a ruined castle where she encounters the most unusual colorful creatures she has ever seen.

World of Warcraft and MLP DO NOT belong to me they go to Blizzard and Hasbro respectively
A World of Warcraft and MLP crossover
WoW set during the Legion expansion
MLP set at season 1 with modifications

Warnings for the following tags.
Gore: Slight dismemberments and occasional blood loss
Profanity: Swear words where appropriate
Violence: I don't need to explain this
Narcotics: Just some mentioning of alcoholic beverages and slight consumption

Kel'Thuzad is many things. Necromancer. Teacher. Advisor. Former Raid Boss. Trusted friend and vizier to the Crystal Empire's Royal Couple. But in all his experience, he has never had the opportunity to attend court. In this small side-story to the Crystal Vizier, the Archlich finally gets his chance to show his... methods.

This story is a sequel to Dead Heart

After the incident on Nightmare Night, Jonathan has adjusted to life in Equestria - but he misses his magical abilities. So he returns to his homeworld to get a wand, right into the middle of the undead lands. Twilight Sparkle and Arcus Tangens, eager to strengthen the new bonds of friendship, join him on his quest. They have no idea how valuable their discoveries are and how far both the living and the undead will go to use them to their advantage...

3rd installment of the Twilight Goes to Dalaran series.
Knowledge of World of Warcraft is not necessary to understand the story.

This story is a sequel to In Want for a Wand

On his search for Twilight Sparkle, Darren Houndslayer discovers King Sombra's horn and unwittingly resurrects the tyrant. He soon wonders if it might be better to reform an evil king instead of killing him for good. Darren struggles to find his place as a former Death Knight in pony society - but he finds himself confronted with his past by a young colt who develops dark powers that are disturbingly alike to Sombra's...

4th installment of the Twilight Goes To Dalaran series.
Knowledge of World of Warcraft is not necessary to understand the story.
WARNING: Spoilers in the comments!

After being pulled from his nearly nine-hundred year stretch of hell in the dark abyss that is the Twisting Nether to serve the new Lich King, the Archlich Kel'Thuzad was faced with the dilemma of freedom from his bindings to the Scourge. He had been an advisor and (somewhat twisted) friend to the most evil being in Azeroth's history for nearly 15 years. He had butchered and enslaved thousands, spit in and stepped on nature's face with the necromantic horrors that were created aboard Naxxramas, and was a generally annoying raid boss, all while under the cruel tyranny of Azeroth's previous Lich King, Arthas Menethil...
But, when an Equestrian Lich King is appointed by Death himself in exchange for immortality, Kel'Thuzad is in for the surprise of his unlife when he is thrown into a large room, with two comparatively small, sentient equines, who claim to be the reigning Prince and Princess of a kingdom.

This story is a sequel to Seekers of the Epitaph: World of Azeroth

Weeks after the Battle of the Sunwell, human paladin Bella Cartier, night elf druid Flutashe Lunarwind, gnome priest Mena Overclock, dracthyr mage Stellaglim, and night elf demon hunter Raida Lunarwind travel to the northern continent of Northrend in reaction to a series of daring attacks on the Alliance and Horde.

Meanwhile, time runs out for human warrior Jaqueline Pomerton as the magical core within her body draws the spectre of death to claim her life. Though in death, her life truly begins. She will have to learn a new way of fighting while wielding the necromantic powers that course through her.

Other threats will have to be faced as well, from belligerent blue dragons, misguided proto humans, desperate trolls, renegade Titan Keepers and an ancient evil whose whispers bring madness.

Garrosh Hellscream, once a warrior, a champion, and a Warchief, has found himself humbled before, but never quite like this. When Head Dark Shaman Kardris Dreamseeker, fears that the Enemies' numbers will prove too great even for the Kor'kron, she, with the aid of her colleague, constructs a mysterious rune with the ability to teleport the user to a far-away place of which even she knows not. After presenting it to the Warchief as a mere trinket gift, she relocates back to Grommash Hold where she ultimately meets her fate.

Later, when Garrosh and all his loyal forces are utterly defeated, he is given no other choice than to use this rune for his escape. Now here, in this bizarre new world, and guided by an old and good friend, he must undergo new challenges, meet countless new faces, and conquer new obstacles (including himself.) However, the most paramount quests our "beloved" Warchief will ever have need to complete are these: To learn to live in this strange new land, and to make his father proud.

The two Royal Sisters ruled Equestria. They were its Protectors, its Guardians, its leaders, selected by the three tribes. Starswirl the Bearded, he was their mentor, he was there to guide them, he was there to counsel them. Perhaps, they may even view him as their father-figure. Many believed them to be true.

This was not entirely the case.

The Royal Sisters past is something none would venture on to question, how were their life before becoming a Princess, what feat of events that awakened the hidden powers within them? None would know except the King.

Now, the King, the true Guardian of Equestria, has returned. They were bound, not by flesh, but by the bond they shared. He shall return as promised.

Lyra passes out on her way home one night, but when she wakes up she finds herself in a strange realm of fire, ash, and creatures that she could only refer to as demons. Before she meets what she assumes is her end, she is saved by a group of bipedal creatures that take her to their master, someone named Illidan Stormrage. There she learns what the bipedal creatures are preparing for and is offered a choice; either join them or return to her home.

The problem, she discovers, is that there is another displaced pony wandering the land of Azeroth; so she has to choose between a rock and a hard place. She only hopes that she doesn't regret her choice after making it.

(World of Warcraft; Legion crossover with MLP)
(Part of the Universe 13 story series, though reading the other stories is not required)