Chrysalis's 'Mean Six' creations were no match for the Tree of Harmony, which struck them down and rendered them as harmless inert logs … but their spirits had not been completely extinguished. When Gallus and the rest of the 'School Six' stumble upon the logs, they unwittingly release the spirits within. It's up to Twilight and her friends, and perhaps others, to purge the demons from the students.