As Pinkie Pie and Applejack rushed to save Rarity from the awful colors of her magically produced dress, Twilight turned to the cloaked interloper. "What is going on here?"
She pulled down her hood. "Well well well. If it isn't... Twilight Sparkle."
Twilight gasped. "Trixie?"
"What's she doing here?" Spike asked.
Even as he finished, Trixie's red-tinged magic warped him into a little bouncy ball and sent him bouncing off.
With a flare of her own horn, Twilight undid the spell and brought her assistant back. "Enough! What do you want?"
"You and I have some unfinished business. My magic's gotten better since I was here last. And I'm going to prove it! Me and you, a magic duel. Winner stays, loser leaves Ponyville forever!"
Twilight laughed. "Sure thing." Without warning, she called upon the elements of harmony, sending a thick beam of rainbows.
Trixie tried to block it with a shield, yelling "That's no fair! You can't use outside help!" Her shield, though, was pathetic compared to the elements, which burned through it instantly. When they struck her, curiously, they didn't attack the unicorn, but just stripped away and shattered the amulet she was wearing.
As the afterglow of the elements died away, Twilight peered in to see what had happened. "Trixie?"
Trixie winced. "Oh, I had such horrible intentions for you and your friends when I was wearing that Alicorn Amulet. I just couldn't control myself. You can forgive me, can't you?"
"Hmm. Sure."
She smirked. "Oh, good. Don't you think the Great and Apologetic Trixie is the most magnificent humble pony you've ever seen?" With that, she ran off in an undersized puff of smoke. She stumbled once, but quickly recovered and continued running away.