Solitary Locust

Is a My Little Pony Friendship Is Magic (Animation) found here http://www.fimfiction.net/story/59019/solitary-locust. After the royal wedding there is a concern throughout Equestria of changeling infiltration. Twilight preforms a presentation for Ponyville to help them know how to handle the changeling threat. In the conclusion of the presentation, she preforms a very difficult spell (difficult for ponies anyways) that is capable of rooting out changelings, to calm the locals by showing them that there are no changelings among them. Then something went horribly wrong (or maybe Gone Horribly Right). Twilight is left in the alien body of the enemy in front of everyone. Panic ensues and now the town is on a changeling hunt.


 * You Make Me Sic: Twilight does this, (kinda). Instead of correcting someone’s grammar, she berates someone (Spike) for using “that kind of language in this library”