Lunaverse

The Lunaverse is an alternate reality version of Equestria created by through the use of her Chrono Trigger spell and the Cutie Map.

History
The history of the Lunaverse was presumably identical to that of the main timeline of Equestria up until the day on which the Mane Six were supposed to receive their Cutie Marks. Starlight Glimmer, seeking to prevent this from happening, traveled back in time, but was pursued by and. Twilight had already witnessed two other alternate timelines as a result of Starlight's alterations to the past, and thus engaged her in battle in attempting to prevent a third. Unfortunately, the young and many other  foals were distracted by the battle, thus halting the race in which they had been taking part.

This change in history resulted in a timeline in which Nightmare Moon returned and defeated Lunaverse Princess Celestia, whom she then exiled to the Lunaverse Moon in her place before bringing about eternal night. The Lunaverse Castle of Two Sisters was rebuilt to serve as her fortress, protected by a force of Bat Pony royal guards including Lunaverse Rainbow Dash. Lunaverse Rarity evidently served as the castle's decorator, and was the first pony encountered by Twilight and Spike when they arrived in the altered present. After overhearing her talk about the circumstances of her arrival, Nightmare Moon forced Twilight to lead her to the Cutie Map, intending to use the time travel magic herself to find the Elements of Harmony and insure her eternal reign. However, Twilight managed to escape and travel back in time yet again, presumably negating this timeline in the process.

My Little Pony (Gameloft)
In Gameloft's "The Cutie Re-Mark: Lunaverse" event, Sweetie Belle learns of the Lunaverse timeline from Starlight Glimmer while the latter is working at the School of Friendship. Based on a lack of information provided by a reluctant Starlight, Sweetie Belle imagines that the Lunaverse versions of her sister and Rainbow Dash aided Twilight in battling a Nightmare.

Behind the scenes
Little is known about how the history of the Lunaverse unfolded differently than that of the main timeline. This reality presumably involved Nightmare Moon escaping her imprisonment on the Moon in an alternate version of the events of Friendship is Magic, and the absence of the Mane Six in this timeline allowed her to conquer Equestria.