Red aura on Trixie horn, it must be Alicorn amulet effect.
Trixie was lucky Twilight found a way to make her take it off, because if Celestia would arrive and find out that Trixie captured Ponyvile by force, wear corrupting amulet, and that her student was banished, Trixie being thrown into dungeon or banished to the moon or sun would be the least of her worries.
Wonderful technical mastery of your medium. You captured the emotion of Spike, Trixie, and Twilight very well with the facial expressions. The dark, misty atmosphere adds further emphasis on how dire the situation is.
I should point out that, unless intentional, either Twilight's legs are too long, or her body is too shallow. Otherwise, and absolutely stunning piece of art!
I can't wait for tomorrow! Then I need to wait quite a few hours for the HD upload xD I'm sketchy about watching the new episodes on my TV. And I like watching the whole thing without commercials every 6 minutes xD