I got an idea for the game, as more humans exit the arena, the round number increases, as the firewall on the exit is increasing. Also as the 5th human is about to leave there will be a "defend the door" type round were if the head gets to much damage it disappears and the robots kill you for trying to escape.
Also as a 2nd ending if you hit the emperor X amount of times with the bow, he will become a boss. Kill him and a second ending will appear.