The War Of The Ember in the titular last book, no doubt. It has all kinds of animals in the kingdoms fighting against the Pure Ones in one last fight for justice. Especially when Soren offs both Nyra and Striga when the latter kills Coryn.
The Burning also has Soren fighting against his brother Kludd for the last time. Soren's been cornered by Kludd and realizes that he has to kill the Pure Ones leader if they were to save all the owls, but he's also scared of killing his own flesh and blood. But he doesn't have to do it: Twilight does it for him.
"Well, SPRINK ON YOUR SPRONK!!!" Said by Otulissa.