As already mentioned the main driver is energy. Energy is represented by the Energy Spheres, which are logically and visibly located in the front of the boots, on top of the portal and in the weapons. They also serve as indicators of energy status and unit affiliation. Your energy is the color blue and the robot energy is the color red. You don't kill anyone in the game, you only take energy. This is transferred between players, attacking bots, weapons and the portal. The goal is to hold on and fend off attacks from bots trying to drain your energy. If players manage to hold their position, they can use the charged portal to move to the next planet(higher level).