This is another idea based on the ‘Cutie Re-Mark’ episode of Season 5 and a follow-up to Midnight Sparkle Sagittarius.
 

 
In an alternate timeline, Sunset Shimmer succeeded in obtaining the Element of Magic and transformed into a frightening demon. Overcome by the dark and negative influence of her heart, she seized control over the entire student body of CHS without regret, turning everyone into mindless zombie slaves. Once she had gathered enough, she turned them all into ferocious demons and launched a surprise attack against Equestria.  
Despite her attempt, Sunset and her minions were eventually driven back through the portal by the combined efforts of Celestia, Luna and Cadence, as well the Crystal Guard.
 
Trapped for another 30 moons in the Human World, Sunset turned a setback into an advantage by taking over the Human World instead. Within a short period, the Human World had been turned into scorched wasteland with billions turned into either demons or slaves.
 
 
Over the years, Sunset spent her time patiently studying the portal before one day finally unlocking its secrets. With the ability to open portals, Sunset now uses it invade the kingdoms of Equestria, with the magic of her crown and a horde of demons at her disposal.
 

 
 
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