/butcher gets rid of all entities in the worlds. This includes items on the ground, mobs, and item frames.
Butcher does not affect entities that are in chunks that have not been loaded in a long time, I believe. If a chunk hasn't been loaded for a year and a mob was in there the last time it was loaded, the mob will not be affected. If a user reloads the chunk and /butcher happens when the user has left the area, I believe the mob will be killed. I don't know if this is true, but I believe this is how it is.
omg, lucky you! I have always wanted to find either a wild horse, or a horse that got loose! I always rescue horses. Mainly for free or a small money amount. It would always be helpful if you can spread the word about my tiny organization. revanrose6