You mean why they are separated into different files? Background 1 & 2 is just a subtle difference but the rest of the backgrounds are for parallaxing.
Viewing post in Viking & Zombie Sidescroller Game Kit comments
Ah, now I understand. Yeah, thats just to show the animation for fire breath working together with the burn effects for zombies. The background is from when we started creating the assets and we didn't like how the background looked in combination of the Viking so we changed it to the one you can find in the backgrounds folder. (You can also see our first version of the zombie on that animation sample.)