A ponification of The Elder Scrolls II: Daggerfall's cover
Story
The Crystal Empire is a main setting of FIM since Season 3, The player is sent here at the personal request of Princess Celestia. She wants the player to do two things. Firstly, the player must free the ghost of the late Prince Shining Armor from his earthly shackles. Secondly, the player must retrieve a letter from Celestia to a Royal Spy in the court of The Crystal Empire. The letter reveals that Shining's mother, Twilight Velvet, knows the location of the Mantella, the key to resurrecting the first Numidium. The princess wants her spy to force Twilight Velvet into revealing the location of the Mantella so that the Royal Guards can finish the reconstruction of the Numidium. Through a series of mishaps and confusions, the letter fell into the hands of a griffin by the name of Grandpa Gruff. Gruff, not knowing what the Mantella is, consults Chrysalis, the Queen of Changelings (the leader of said Changelings). During this time, the Underprice, who originally destroyed the first Numidium because of its misuse by Twilight(The one from G1), is recuperating deep within a tomb of The Empire, after expending so much energy destroying it the first time. In order for the player to give the Mantella to anyone, the player must kill king Shining's murderer and put his ghost to rest. After accomplishing this, the power of the Mantella restores the Underprince's power.
Endings
Equestian Scrolls II: The Crystal Empire has six different endings:

If the Hero activates the Mantella themself while in possession of the Totem of Twilight (the controlling device of the Numidium), the Numidium will slay the Hero, go out of control, and be destroyed by Imperial forces.

If the Hero gives the Mantella to the Underprince, he absorbs its power, passes into eternal rest, and creates a large "magic power free" area around himself.

If Gruff is victorious, he uses the Numidium to destroy the Equestrian forces and the "Bay Kings," the "rulers" of the several kingdoms of Equestria. The Underprince arrives shortly thereafter to destroy the first Numidium once and for all, losing his own life in the process. Gruff then succeeds in creating Griffonstone, a kingdom of Griffons.

If the Royal Guard are victorious, they succeed in recreating the first Numidium and use it to defeat Cadence and Flurry Heart, defeat the Griffons, and to unite all the Kingdoms of Equestria under Celestia's rule once again.

If Cadence and Flurry Heart win, because they are salty Shining died they use the first Numidium to kill all the other rulers(Even Celestia and Luna) just before the Underprince destroys it and himself.

If Chrysalis receives the Mantella, she uses it to make herself a god.

Continuity
Since The Crystal Empire has six very different endings, It is revealed in books in the sequel The Equestrian Scrolls III: Everfree that at the end of The Crystal Empire, an event known as the "Warp of the West" or "The Miracle of Peace" had occurred, that is, due to the fact that in order to retrieve the Mantella, the Hero of The Crystal Empire must enter Tartarus, a disruption was caused in space-time. Therefore, all of the endings of The Crystal Empire occurred simultaneously, such a powerful event made the hero vanish, and changed the Crystal Empire in many ways.

However, in The Equestrian Scrolls IV: Tartarus, treasure hunters claim to be hunting for treasure on behalf of Griffonstone and Grandpa Gruff.
If you want me to ponify the other Elder Scrolls, I can do so, I even have names
The Equestrian Scrolls: Equestria
The Equestrian Scrolls II: The Crystal Empire(You're here now)
The Equestrian Scrolls III: Everfree
The Equestrian Scrolls IV: Tartarus(Set in Canterlot and Tartarus)
The Equestrian Scrolls V: The Dragon Lands(Fitting, huh?)