This story is a sequel to Sombra visits Skyrim

Nightmare Moon, formerly called Princess Luna, casts a spell that should, in theory, let her leave her moon and return to Equestria. When the spell misfires she finds herself in a strange new world, surrounded by strange new creatures. After a few weeks of fighting in the Arena she meets a group of unlikely heroes that are on a mission given to them by the Emperor himself. She embarks on a journey that will take her through the pits of Oblivion itself and forge new friendships along the way.

But will she be able to stand up against Mehrunes Dagon and his Mythic Dawn cult, or will the power of the Lunar Princess fail her when she needs it most?

Inner Wisdom and his friends reunite after three years of being apart. Their reason; find the werepyre, the one who cursed Peachy and Tick, and reverse what had happened. They have to track down long lost clues that will lead them to the creature and beg the Gods themselves for their help.

While they hunt the Beast down he is roaming around, hiding in plain sight as he taunts the would be hunters.

The question is; will Wisdom and his friends find the courage to face the Beast in open combat? And, if they do find the Beast, will they have the nerve to actually kill him?

(Final installment of The After Party storyline.)

Four friends awaken after the most epic party of their lives to find that they have somehow landed in Equestria! But they landed in the center of Canterlot. They must figure out how they are going to live their new lives and fast. Of course that doesn't mean somepony isn't going to notice the new arrivals.
A normal adult earth pony with no cutie mark
A bald adult unicorn whose into music
A adult pegasi who loves to read
And an adult unicorn with a pegasi name

(Takes place after the end of Season Three)

Princess Darkstar, the feared ruler of Shadowlot, has returned and now it a teacher at the School of Shadows.
Sweetie Belle, the former holder of the powers of Thrack, has lived in peace knowing the demon was destroyed.
What will the two of them do when Sweetie Belle's true Shadow shows itself to everypony in both worlds?

(The third and final installment of the Dark Crusader series. Sequel to Sweetie Belle and the School of Shadows)

Rocket Sky, Peachy Keen, Inner Wisdom, Tick Tock, and Rose Petal return for a second adventure a year after the events of The After Party.
Rocket is King of the Changelings alongside his wife Rose Petal, Wisdom is an adviser to Princess Celestia, Tick is trying to become a great musician, and Peachy is having fun learning from Princess Luna. But after the war game they take part in they discover there is a poison coursing through Rocket's veins and its slowly killing him. His friends must find the cure before it is too late and save the king of an entire nation.

Sequel to The After Party.

Jak never found it odd that he and his sister Pinkie were different from everyone in their village, despite the fact that their friend Daxter pointed it out from time to time. Nor did to the trio find it odd that Jak and Pinkie were raised by Samos the Sage, along with his daughter Keira. Jak never questioned how odd their life was, even when he and Pinkie slowly developed the skills necessary to protect themselves from any dangers the world might throw at them.

Pinkie, on the other hand, knows that there are secrets hidden deep in their past... secrets that will change how she and her brother look at the world around them, while fighting to protect it from those that would seek to do it harm.

(Jak and Daxter crossover)
(Part of the Universe 13 story series, though reading the other stories is not 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)

Sunset Shimmer almost succeeded in taking over Canterlot High, stopped the Sirens from taking over her new home, and managed to prevent the destruction of two worlds. She feels that she deserves a break and decides to return to Equestria during her summer break. Unfortunately, when she enters the portal she appears in a land that is different from the worlds she's already been to. Now she has to save this world before she can even focus on returning home.

Unfortunately, she's not the only Equestrian that's appeared in this new world, as one of Equestria's most dangerous villains is loose to do whatever he pleases. How will she cope with having to save this new world from Tirek?
(This is a different Skyrim story than my Sombra visits Skyrim story)
(Part of the Universe 13 story series, though reading the other stories is not required)

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)