I usually see depictions of Celestia, Luna, Queen Chrysalis and Discord as some sort of group of four gods, as if they were on the same level. Needless to say, Discord kind of ruins the pattern. I think the Windigoes should have a Queen/Princess of their own, they pretty much complement the Changelings.
So similar to the yin-yang with Celestia and Luna from the first episode, here we have a cycle involving both Windigoes and Changelings feeding on ponies feelings. When the Ponies are protected from the Windigoes by the Fire of Friendship, the changelings feed on their love. Eventually, like some kind of self-defense mechanism, they start distrusting and even hating each other, their hearts becoming cold, and so the Changelings have no choice but to flee. Then its when the Windigoes come and feed on their hate, until they start trusting and liking each other again. And so on. Sometimes it sucks to be a pony.