I really loved the episode, best one this season. Easy A. Tons of good stuff in it. Funny magic, reestablishing pony lore (s1 reappearances), great pony faces/expressions, Fluttershy was great, all the mane 6 in it, Zecora as Yoda, nice pace, generally felt like a season one episode for some reason, I also liked the line: "That's not magic, that's just Pinkie" and the fourth wall breach at end, etc...
I liked Trixie as the villain in the episode. Half of her behavior was her personality half was the "evil" amulet. Which wasn't evil in itself IMO but was more along the lines of "power corrupts", particularly that things can go messy, and that power corrupts especially when it's beyond one's own abilities (as was in this case) not just one's moral standing.
That's why she was forgiven (although not completely like: "aww, we forgive you, group hug", but more like: "hmm, we'll give you a second chance, don't mess it up"), without the amulet she wouldn't have been this big evil mean meany, but just the petty and boastful fraud meany. As far as the apology at the end, I think it was true to her character because it wasn't really an apology, even within it she stayed petty and boastful still trying to be the best at something, being the most humble... Oh wait, paradox...
I did predict Twilight's and Zecora's deception idea as soon as the second duel started but it was executed really nicely and a great idea involving "the power of friendship", so...
Awesome episode.