Sunset Shimmer decided to escape punishment by escaping through the dimensional barrier. She thought long and hard about doing this. She decided that she would begin a new life in a new dimension and forget everything about her past life as a pony in Equestria. There was nothing left for her here, and she didn't want to kill herself or become an outlaw. In a new dimension, she could rebuild her reputation and become a powerful magician or at least someone with a high social standing.
She prepared herself. She packed some supplies in a bag and gulped. She then closed her eyes and ran into the portal. The next thing she knew, she was surrounded by a blinding white light.
Sunset Shimmer arrived in the human world in her actual human form's house. She quickly looked at her body and said, "I look absolutely stunning for a human! I'll fit in great!"
She quickly looked around and sat down on a couch thinking about what to do. "So if I have a human counterpart," she said. "What do I do with her?"
She then heard a door open and she ran into a closet. She heard her human counterpart return home alone from a party with her friends. She sang under her breath while Sunset looked in the closet and found a knife. She then had a devious idea about how to handle with her human counterpart.
As Human Sunset began to watch TV in the living room, Sunset slowly walked out. She quietly approached from behind.
Then, she grabbed Human Sunset on the neck, dragged her to the house's basement and said, "Oh hello, counterpart. It's about time we met."
She found some rope on the floor and tied Human Sunset to a chair. She said, "What do you mean by counterpart?! Please, just let me go!"
"It's simple. You see, I am your counterpart in a world where I was a pony. Unfortunately, I was punished," said Sunset. "I was punished for doing a crime that caused Princess, or should I say Principal, Celestia to not pick me as her student. Now that I'm here, I will take your place. I know EVERYTHING about you. As for your existence, I will make sure you are replaced."
Human Sunset screamed as Sunset first cut off her right ear with the knife. She then let out an even more horrifying scream as Sunset proceeded to stab her in the knees, rendering her immobile.
Sunset said, "Hush my dear. It will all be over soon." She then slashed Human Sunset's throat, silencing her and spilling blood all over the place.
Human Sunset then got stabbed 6 times in the chest, killing her. She finished the job by decapitating Human Sunset. She said, "There... She's gone..."
She then gasped and realized what she had to do: She had to dispose of the body and remove all traces of what happened.
She quickly used her magic to clean up all of the blood as well as remove her fingerprints from the knife and rope and stuffed her body in a bag in the basement. She then threw the bag into the house's furnace.
Within 42 minutes, there was only a pile of ashes left in the furnace. She quickly raced upstairs and changed her clothes. She then used her magic to completely remove any traces of blood on her clothes and began her life as this dimension's Sunset Shimmer.
When her parents returned home several hours later, her mother said, "Hello honey, we're home. How was your day?"
"Great, mom," Sunset said. She then laughed manically in her room, realizing what she had done. She had truly gone off the deep end.
AFTER THE MOVIE'S EVENTS
Sunset Shimmer had mixed feelings about what had happened. She was saddened that she could never return to Equestria, but she was happy that she was forgiven by Twilight. She was ready to begin a new chapter in her life, a better one were she contributed positively to society. It seemed as though the Mane 6 in that world would become the Mane 7 or even 8 if Flash Sentry was counted
She was sitting behind the school afterwards when all of a sudden, a glowing apparition of her former Human Self appeared in front of her with a pocketknife. She said, "They may forgive you, but I never will..."
Ghost Sunset then stabbed Sunset in the right eye socket and cut out her right eye. She then ate it in front of her and said, "Hehehehe... There, I had my revenge.... Now you'll live the rest of your life as a disabled freak! Never will you get the popularity you desire, nor will you get the friends you want. Bahahahaha! But I still have one more thing to do."
She then pulled out a gun and shot Sunset in the kneecaps, destroying the use of her legs. She then took her arms and said, "I see you like these arms of yours, you little slut. How about I smash them into pieces like you did to me?" She then broke them, causing Sunset to scream in pain. Human Sunset laughed as Sunset screamed in pain.
Sunset was then kicked several times in the stomach before getting her right ear cut off by Human Sunset's knife. She then punched her in the face and said, "I bet you fucked all the jocks with MY body, you whore! You disgust me! How about I amp it up?"
She then took her gun and shot her hands clean off. She then said, "Hehehehe, I guess you're the fake. Take care."
She then took her gun and shot her in the stomach, finally killing her. Sunset Shimmer was dead. Human Sunset Shimmer laughed and then walked away.
2 hours afterwards, the Human Applejack and Celestia were walking and talking about the day's events when Applejack screamed, "Jesus Fucking Christ, who did that to Sunset Shimmer?!"