To spite the merry season of Hearth's Warming, Trixie exacts her revenge on Twilight for her humiliation after the Ursa Minor "incident." At least she would, if somepony hadn't interfered.
"When the dust has cleared, and victory denied; a summit too lofty, river a little too wide. If we keep our pride, though paradise is lost, we will pay the price, but we will not count the cost."