bonus passive helped ensure victory

I beat Zunta with "Lil' XT" and "Darkmoon Cub". I started with "Lil' XT", taking advantage of the mechanical revive passive before switching to "Darkmoon Cub" where the beast damage bonus passive helped ensure victory.
or wow
I'm a bit confused though... is this a just for fun thing or was I suppose to earn a specific reward because I received only that usual handful of gold and exp?