This has very little bearing on the 'Animorphs' series proper, but it is still a fascinating science fiction epic.
The powerful Ellimist is revealed to have originally been Toomin, a member of a peaceful race who live to perfect their floating crystal home and game with each other. The game involves hypothetical situations and worlds and making changes to promote or eliminate species.
A series of disasters puts Toomin on the path to become the being the Animorphs encountered and the origin of his dispute with Crayak is revealed.
A lot of fun and worth reading - there is a hint of what's to come in the framing narrative of the story, but no true spoilers to prevent a reader from reading this before finishing the rest of the series.
Next: 'The Return'
Previous: 'The Resistance'