Twilight's a good witch. Go read a fanfic about her below, along with Turmoil Rising.
Description:Twilight Sparkle rules Equestria as the new sole monarch. Three years have passed since her coronation and the kingdom had enjoyed a time of relative peace under her watchful eye, while she and the rest of her friends went on to live their own separate lives without losing contact or forgetting their friendship.
But even with everything running smoothly, in the world of light there will always be a shadow that lurks beneath. The ancient primordial darkness of Equestria, which was believed to be a little more than a fairy tale and known only by those whose lifetime transcends the Two Sisters, is about to re-emerge and has found itself agents through whom to execute its will.
Will the power of friendship be enough to stop the darkness, when there is no light to take its place?
[Adventure][Comedy][Alternate Universe]
Author: Epsilon-Delta
Description: Seeking fame and fortune, Rainbow Dash sets out to defeat the legendary witch Twilight Sparkle and collect the five hundred million bit bounty on her head. The one thing she wasn't counting on was Twilight being less evil than she expected.
A Witch in Broad Daylight (New Part 38!)