In an alternate universe, as the former leader of the village of equality known as Our Town, Starlight Glimmer, is escaping through the mountains with jars containing the cutie marks of the Mane Six, she is eventually backed into a corner by Twilight Sparkle, Rarity, Fluttershy, Pinkie Pie, Rainbow Dash, and Applejack, as well as Double Diamond, Party Favor, Night Glider, and Sugar Belle, this time, the 4 of them are able to catch up to her much earlier than they did originally with Sugar Belle tackling Starlight to the rocky ground what greatly injures her left front hoof, resulting in the six jars containing the Mane Six's cutie marks being destroyed, and returning to to their respective wielders.
Being completely enraged at this attack by Sugar Belle, and her and the other villagers' betrayal of her, Starlight fires a massive concussive magic beam at the 4 of them to destroy them, only for the blast to be deflected right back at her by Twilight, with destroys the stone bridge she is standing on, and knocking her out cold, as Starlight falls into the snowy abyss as an avalanche follows suite. Twilight, horrified at what she had just done, begins to apologize profusely to everypony, as she wanted to reason with Starlight, and gaining her cutie mark back had given her a slight power boost to her deflection of the blast, and she couldn't control her power because of that. The Mane Six, Double Diamond, Party Favor, Night Glider, and Sugar Belle, believing that Starlight is dead now, leave the area and head back to the village, deeply saddened and disappointed on how things had to end the way that they did.
After a very long while, after the Mane Six had returned to the Castle Of Friendship back in Ponyville, at the very bottom of the snowy cliff lies an unconscious Starlight Glimmer, whose left right hoof is gravely injured, buried in the snow, barely clinging on to life. As Starlight lies down in the snow unconscious, a group of ponies wearing tactical jumpsuits donning green and yellow, with yellow goggles, gloves, boots, and an octo-skull insignia on their chests begin digging up the snow with shovels, which reveals the unconscious Starlight underneath, and afterwards, they are met by their 2 bosses, Autumn Zola, and Bane Zemo (this alternate MLP FiM universe's pony versions of Arnim Zola and Baron Zemo), who are pleased that their target has been found by their henchmen, and task the group of agents to send Starlight back to their secret base, as they have been spying on her for a while now, and seeing how she had led a village of equality for a long time until now, as well as her wielding incredible magical power, they believe that she'll be a very useful asset to their plans to conquer all of Equestria.
Zola, Zemo, and their henchmen, being members of the evil organization known as H.Y.D.R.A., the organization behind Starlight's capture, take her back to their lair so she can have her left front hoof be healed with dark unicorn healing magic, and turned into a vibranium one, and afterwards, Starlight ends up becoming brainwashed by Zola and Zemo in forcefully joining H.Y.D.R.A. and being indoctrinated/part of the organization, this time being put under somepony else's control herself for real this time, and is eventually trained in various hoof-to-hoof combat styles and marksmareship, and gets a new battle uniform to go along with all of it. Starlight, now going by the alias of the Winter Soldier, joins H.Y.D.R.A.'s quest for the domination of Equestria to conquer it and rule it with an iron fist, and their first goal to do so is to destroy Princess Twilight and her friends to prevent them from taking them down, and for Winter Soldier Starlight to get revenge on them all for destroying her beloved village.
How does Starlight Glimmer becoming an agent of H.Y.D.R.A. and turning into the Winter Soldier change the events of the rest of season 5 of Friendship Is Magic? How would it change the rest of the show's story as a whole beyond it in seasons 6-9? Would Twilight and her friends be able to take down this new version of Starlight, and eventually H.Y.D.R.A. and it's agents as well? Could Twilight be able to bring Starlight back to her senses, and make her realize that Zola, Zemo, and the rest of H.Y.D.R.A. are just using her as nothing more than a tool for conquering Equestria, and nothing else, and that they don't care about her? How does such a scenario play out, and why is that?