The ponies in Starlight's old village had moved on from the fact that she was not in control of their town. All but one, named Quill. He was the only one in the village who kept his equals sign and had tried his hardest to get everyone else's back on. With a sacrifice, he gains the magic to steal others' cutie marks and uses torturous methods to get ponies to conform. Looking for Starlight, he comes upon Ponyville. He takes over and seeks to expand to Canterlot and Cloudsdale. With no one to help them, the Mane 6, Starlight, Discord, Spike, and the CMC's form a resistance against the cult.
Set mid-season 7.