Speculation on 'Magic Duel' - The Elements of Chaos · 5:47pm Nov 21st, 2012
I suspect that Trixie's gorget will turn out to be one of Discord's six Elements of Chaos that he built during the Era of Chaos but never had a chance to deploy against the alicorn sisters. Trixie's is the Element of Egotism, the opposite to Twilight's Element of Friendship/Magic. Sombra found it and used its magic as the basis of his tyrannical rule and now it, and the corruption of the soul that it brings, has passed to Trixie.
I can see the following outcomes for the episode: