Twilight knew of other sentient species on her own planet, Twilight knew of life in other dimensions, what Twilight didn't expect was there to be life from other planets. She especially didn't expect that life to be already invading Equestria.

Set straight after the ending of Season 3, Animorphs: The Symbiosis is an MLP / Animorph crossover that won't, at first anyway, feature the Animorphs at all. Instead, it focuses on the Yeerks, and the interplay between the Peace movement, and the rest of the empire.