The notes on impure world reincarnation ,'Say whatever about his morals that guy is still a genius'. I looked at his notes and my understanding of the technique increased,the Summoning: Impure World Reincarnation binds the soul of a deceased person to a living vessel, restoring them as they were when they were alive in order to do their summoner's bidding. It was originally created by Tobirama Senju. This technique used a seal which acts as a gateway for the soul of the target to cross the borders of the pure realm and reside temporarily in a body. But due to it just being a gateway full powers of the deceased can not be brought over by the original technique. Orochimaru, being the genius he was, managed to change the seal after doing extensive research in seal and summoning, to gain the ability to actually summon the souls and bind them with talisman to gain almost the same amount of power as they had during that prime. He actually managed to restrict the amount of power with one could be summoned as he was planning to summon the rest of the hokage's at 10% of their power. Even though i was angered by his audacity to think he can control my dad, I know he would fail and quickly read through the rest of the notes.