Twilight Sparkle is the former self-proclaimed princess of the Plunderseed Kingdom, Princess Celestia's former student and the main antagonist of Ed, Edd n Eddy XL: The Aperture War. She is voiced by (as you know) Tara Strong.
While normally portrayed as a heroine in My Little Pony: Friendship is Magic, her EquesDeSacEntertainment.com incarnation is notoriously different from her actual self. She appears exclusively in the show's theatrical film, Ed, Edd n Eddy XL: The Aperture War acting as how she is in the MLP: FiM franchise. But it's later revealed in the movie that she was actually a sinister and deceiving sorceress who made the Eds think Trixie started the Aperture War, when really she was the one behind the chaos. She continues to do this, until after the final battle, Edd redeems her.
The real Twilight Sparkle is usually kind and friendly, while the parody Twilight is sadistic, vindictive, manipulative and cruel. However like her real self, she is highly intelligent. The parody Twilight uses dark magic instead of good magic. While the actual Twilight wants to bring peace and harmony to Equestria, the parody Twilight wants to bring pain and misery to the Eques-De-Sac. Indeed, the Ed, Edd n Eddy XL version of Twilight Sparkle is very evil, unlike the real Twilight from the series.
Ed, Edd n Eddy XL: The Aperture War
Twilight Sparkle is first seen arriving in the Eques-De-Sac to warn the Eds about Trixie spreading the rumor that has caused the Foullands and the Breakfast People to declare war on each other. She tells the Eds to embark on a quest to end the war before the Fourth Kingdom falls under chaos and ruin. Later on when she arrives in her castle, she tells Kevin and Eddd that her plan had finally worked. She manipulated the Eds and made them think that Trixie started the war. She then proceeded to corrupt the Element of Magic and transform herself into the true monster she really was. Twilight explains that she wanted to bring eternal darkness to the Eques-De-Sac after the soldiers battled there, so she can take over the Fourth Kingdom without any sign of man or pony. This means that she was the true culprit who started the Aperture War. She wanted to make everyone/everypony (even Trixie) suffer from the carnage that the soldiers have caused during their battles.
When the Eds confront Twilight, she challenges them into a magic duel, just like Trixie did earlier in the film. Twilight's final strike was to kill the Eds. But before she could even do so, Trixie comes in and saves them from her. Twilight Sparkle gets surrounded by the three goofballs. Eddy plans to beat her up, but Edd had a different idea. He tells Twilight that she doesn't need to be evil in order to be a princess. Twilight agrees with what Edd says and surrenders. She also promises never to start another war between two kingdoms as long as she lived. Wheatley becomes the main antagonist of the rest of the Ed, Edd n Eddy XL series' run.
"Your faithful student isn't here anymore!"
"More hayburgers, more power! MORE HAYBURGERS, MORE POWER!! *evil laugh*"
"Foolish Eds! Didn't you realize it? I'm the one who started the Aperture War. My plan is magnificent! Genius! The soldiers will take their most daring battle in your so-called 'Eques-De-Sac' and then, Trixie and the rest of those innocent people will suffer. As soon as everyone and everypony has left and there is no sign of man or pony, I will rise to power and the Fourth Kingdom will soon be mine! ALL MINE!! *evil laugh*"
"You can never defeat me, Eds; I will have war! Your idiot friends will suffer and your home will burn!"
"AGH!! Look what you've done! You imbecile!"
"NO! I will not lose to a bunch of clowns, like the three of you!"
"Say goodbye to your 'enemies', Trixie... FOREVER!!! *evil laugh*"
"Well if that's the case,... I surrender."
"Eds, thank you; especially you, Double D. From this day forward, I solemnly swear that I'll never, ever, EVER start another war between two kingdoms again as long as I live!"