Flashback
The mists within the glass orb began to swirl, and a picture slowly began to form. From the haze emerged the vision of a white, rainbow maned alicorn, standing over a yellow unicorn filly with a fiery mane, and a Burning sun cutie mark.
"Thait looks just like Sun Shimmah!" Truly exclaimed. "Ahnd she's with Princess Celestiah?!?"
"Shhhh! I want to hear this!" Moondancer whispered, looking back into the orb.
"Young Sunset Shimmer, I am very pleased that you have decided to become my personal student." The Princess announced proudly. "I hope to pass on to you everything I know about magic."
"Thank you so very much, Princess!" The little filly replied enthusiastically, bowing to her new teacher. "I promise that I won't let you down!"
"Why aren't their lips matching what they're saying?" Zigzag asked curiously.
"Because the spell is translating their words into english, and it's not an exact translation." Moondancer replied. "Now will you please let me listen?"
The images moved forward in time, and the there observing equines saw Sunset grow before their very eyes, growing stronger and stronger in magic each day under Celestia's tutelage. Finally, an angry-looking Shimmer stood before the alicorn princess defiantly.
"Why haven't you haven't taught me everything you know?!?" Sunset demanded. "I want to be stronger!"
"Magic isn't just about strength." Celestia replied sadly. "I had hoped you would have learned that by now."
"The only thing I've learned is I'm done with being your student!" The defiant filly yelled, running out of the throne room. "I'm gonna become the most powerful unicorn that ever lived! I'll even become more powerful than you!"
"Why that ungrateful little tramp!" Moondancer snorted. "How dare she talk to the princess that way!"
"Vould you please be qvuiet, Moondancer?" Gypsy snapped. "Ve are trying listen to ze converzation!"
It was at that point that Sunset Shimmer began looking through books in the Royal library, and using that knowledge, found a mirror hidden away deep in the castle. This mirror was a portal to a pocket dimension, where time flowed differently than in Equestria, and Sunset thought she could go there to study magic and become even stronger than Celestia!
"By the time I return," Sunset growled, lugging a bag of magical textbooks books through the mirror. "I will have enough magic to challenge my mentor, and take over all of Equestria!"
And so, hoping to increase her magical power, the arrogant unicorn filly stepped through... and disappeared! As the mares watched, time passed quickly around the mirror, as the ages came and went. Finally, the arrogant mare came back from the mirror, shocked to see how much of the world had changed.
"W-what's happened to Equestria?!?" A hysterical Sunset screamed, looking around at the ruins of Canterlot. "What happened to my friends, my family?!?"
"So that's how she got to the present!" Zigzag noted knowingly, nodding. "The flow of time difference between the two worlds, must have changed between portal openings."
"This is all Twilight Sparkle's fault!" Sunset Shimmer growled, as she wandered the countryside alone. "I'll never see the world I knew again because of her!"
They watched the filly make her way across the pony communities, from Fort Rainbow Dash to Hoofkaido, playing the part of a simple-minded fool. Eventually she caught the eye of a Stallion, as bitter and angry as herself, and one lifebond later a young unicorn foal was born to them. They saw the filly reach childhood, as the mother trained her to be the living weapon the baby had been birthed to be.
"This is a mind manipulation spell, Sun. while not as good as mind control, it'll allow you to cloud a pony's judgment, making them more susceptible to any radical suggestion you might make."
"No! Don't wanna learn magic!" The filly protested. "Wanna go out and play!"
"NO!" The older mare screeched, smacking the toddler across the mouth, and knocking her to the ground. "You're not going anywhere until you learn the weakest version of this spell!"
"O-okay..." The little filly whimpered, wiping the trickle of blood from her mouth with her hoof. "I'll try harder, I promise..."
"You need to become the best, like I was." The mare snarled, as the four equines watched the little filly grow up with the unhappiest of childhoods. "If your going to Punish ponykind, and destroy Dream Valley- Twilight's Sparkle's legacy- you need to become the best."
The mists swirled again, and they saw a fully grown Sunset Shimmer, standing before her mother's tombstone, her eyes burning with the utter hatred and coldness her upbringing had instilled in her.
"You'll need to be the best, if you are to carry out my revenge."
As the mists in the crystal ball cleared, the four mares only sat there, staring at each other in silence.