Also usually if you are on auto or if you use a mystery without targeting, it will always hit someone with the lowest HP or if it is an interrupting skill, it will stop an opponents skill.
I just did Sage Battfield, I have Kisame in the back.. he is behind a ninja but the person I was battling attacked him... EVERY SINGLE ONE OF HIS NINJAS.
There would have to be a ninja in front of kisame to prevent that. If not then thats what would happen. Or if he had lowest HP all mystery would hit him.