This is based on opinion. Please don't list it on a work's trope example list.
Nightmare Fuel / Total Drama Equestria
The appearance of Grimmore, to Chris and the Total Drama contestants.
Celestia's flashbacks on Tuerto. As time progresses, you can see why the days between April and May of 16 B.E. were forgotten... Basically, Tuerto got a Break the Horseshoe Salespony moment and turned against humans to protect the ponies.
Tuerto only has one eye... enough to parafry (paralyze and petrify) ponies that stand in his way. The other eye socket is empty. Back in the month when Tuerto turned into the villain, his other eye was present, and his other eye was used... to severely injure a human beyond help. Nobody knows what happens if both eyes were combined together...