In the beginning, there were three alicorns - Celestia, Luna, and Fanged Doom.

Fanged Doom was... interesting. He was unique. So unique that his mother didn't even care about properly naming him and therefore gave him a stupid name. Because of his uniqueness, he was banished. Nopony expected him to return - or they wouldn't have, anyway, if they'd known of his existence. He was kept a secret from the general population.

Now, he has returned, and he wants revenge.