During a trip to Ponyville, to relax after a long week of work, Spitfire suddenly finds herself in an unknown world, one that seems broken and filled with conflict, along with monstrous creatures that had to be demons. From that point forward she encounters the Illidari, demon hunters that have pledged their lives to hunting down the demons and ending their burning crusade as they attempt to snuff out all forms of life that exist across the universe, only to eventually fall in with the Illidari to protect her home world from eventually becoming a target of the Burning Legion. Not long after that Rainbow Dash ends up on the same world and together they discover that Illidan Stormrage, the leader of the Illidari, has a plan to bring down the leaders of the Legion and bring an end to their foul crusade, only for fate to throw a couple of wrenches into their plans, forcing them to wait for a number of years before they can act against the Dark Titan and his forces.

Regardless of what happens to them, Spitfire and Rainbow will stop at nothing to bring down the Legion, even if it means getting involved with the forces of the Alliance and the Horde while trying to prevent another war from breaking out.

(World of Warcraft/MLP Crossover, covering both Legion and Battle for Azeroth)
(Part of the Demon War story series, but reading the others isn't required)

Twilight, Starlight, Cozy and their brother Jak, along with their friends Keira and Daxter, spend their days playing around the village, helping the other residents of Sandover whenever they can, working on their hobbies, and occasionally learning from Samos, the Green Sage that calls their village home, even though Daxter often gets him and the others in trouble whenever they do anything interesting. That doesn't stop them from having fun and learning a few skills to defend themselves, all while unaware of the grand adventure that they'll be embarking on in the near future, along with the fact that the fate of the world depends on their actions to come.

(Jak and Daxter/MLP crossover)
(Part of the Demon War story series, but reading the others isn't required)

Sombra, the dreaded King of Darkness, was defeated and his body shattered, but his dark soul survived the return of the Crystal Empire and went into hiding. Some time later it found a path between worlds, a mirror portal, and arrived in a place called Hueco Mundo, where it gained a new body to start a new life. In the process Sombra loses his memories and becomes a shell of his former self, searching for something that he knows that he lost while having no idea where to find what he was missing.

Along the way he somehow finds his way to Karakura Town, into the hands of Kisuke Urahara, and learns more about his new body than he could have learned on his own, before coming into contact with Ichigo Kurosaki and his small group of friends. From there he starts an epic journey to help them save another friend from a terrible fate, fight the people that were in their way, and face an evil that was hiding in plain sight at the same time... along with finding out what happened to his missing memories.

(Bleach/ MLP Crossover)
(Part of the Universe 13 story series, though reading the other stories is not required)
(Also, the story will not include the Fullbring or the Thousand Year War Arcs)

Tirek thought it was over when the mares he thought he had defeated used the powerful rainbow power of Harmony against him, stripping him of the power he had stolen from the ponies of Equestria, while no doubt sending him back to his cell in Tartarus. Fate, however, seemed to have other plans for him as he found himself buried under the ground, in a shallow grave that he had to pull himself out of, just as a bell tolled, and in a foreign land that he knows nothing about. At the same time he discovers that he wasn't the only one buried, as a fallen warrior also pulls herself from the grave and sets off on her own personal quest, while also finding out that they are both undead in some manner and that fate has big plans for them.

He and his unlikely companion must band together for the foreseeable future and tackle the dangers of this world, all while Tirek searches for the power that will allow him to break his condition, regain his true power, and then conquer the world, or die trying.

(Dark Souls 3/MLP Crossover)
(Part of the Demon War story series, but reading the others isn't required)

Chrysalis has heard rumors of a crystal mirror having the power to take ponies to other worlds, where they gain powers that put them on par with the likes of Princess Celestia or even the Spirit of Disharmony himself. She wishes to use the mirror for her own ends, so she can gain the power to finally have her revenge on the ponies that have taken everything from her and maybe regain her empire in the process. The world she finds, however, is the dark interior of a ship that is being overrun by dead creatures that will stop at nothing to kill her and the repair crew that came to fix the ship.

She must quickly get used to her new body while fighting the hordes of the dead, come to terms with all of the horrible decisions she has made over the years, and maybe see the light that the ponies talk about... provided that she, and her new companions, don't get killed first.

(Dead Space/ MLP Crossover)
(Part of the Universe 13 story series, though reading the other stories is not required)