20 years after the CHS girls' graduation - and the tragic passing of their friend Sunset Shimmer, Professor Twilight Sparkle and Spike found Sunset's journal, with a message from herself... "Please help Sunset." [Rainbooms vs Mane 6]
Alicorn Princess Twilight Sparkle, aka 'Princess Amicitia', bond by the rule to never meddle with free will or reveal herself, seeks to help ponies find happier endings in the multi-verse most infamous grim dark worldlines. Some wins, some losses.
Starlight and Twilight drink a potion which reveals the downward spiral one of Starlight's alternate universes took. Meanwhile, Twilight watches Starlight take a downward spiral of her own.
A few months prior, Starlight Glimmer drank a potion which showed the tragic demise of one of the worlds she affected when she sabotoged the first Rainboom. Now, she must undo the damage she's caused before it can get any worse.
Nightmare Moon spent a thousand years alone. After returning and overthrowing her sister, she finds a possible companion in one of the ponies who sought to defeat her. Now Rarity must fight alone to retain her sanity.
Twilight Sparkle and Starlight Glimmer are engaged in a time travel battle and no matter what she tries, Twilight just can't get Starlight to stop altering the past. The battle is growing old for Starlight so she decides to end it once and for all.
Starllight Glimmer has won, she has made Equestria into her world where no pony is different where everypony and everything is the same. Everypony never feel down, with Starlight controling Equestria only four still have their normal cutie marks.
When you find yourself stranded in a timeline where Equestria isn't doomed, is it still moral to rewrite history to restore your home timeline? (Season 5 Finale)
Battling Starlight Glimmer, Twilight finds herself in another alternate timeline. Only this time, she finds herself in the Golden Oak Library with the Princess of Friendship: Sunset Shimmer.
In the land of Equestria, there are no differences, no heartache, no progress, no purpose. There is just life, and whatever comes after. Everypony is equal. Starlight Glimmer won, but she may have also lost.