Before we continue with Decidueye and Lopunny's search for Cinderace, we need to know a little bit about their (at least Cinderace and Decidueye's past)

Cinderace is a good fighter, both with weapons and for his own skills but his "trainer" still sees him as weak compared to Decidueye, his star pokemon.

She has advanced and impressive reflexes and a more practical and flexible handling with weapons and skills, seeing herself superior to Cinderace from the eyes of that "trainer"

And as you can see, they dont do normal fights but illegal ones where everything is allowed.