The alternative method to kill someone in the past was to make a single attack and let it flow into the past like a stone rolling across the floor. He would only need to spend energy once, but because the attack lacked continuous support, the friction created from hitting and killing the past versions would slow it down.
Even if each past version could only slow down the attack by one unit, one second of work would remove 1.855 × 10^43 units of power from the attack. Eventually, the attack will grind to a halt.
This was the method the guardian used to kill his past versions. It was a single attack, yet it mowed down versions of his past for days because of how weak they all were.
