Summoning: Impure World Reincarnation

This summoning is a forbidden technique used to revive the dead. Kabuto mentions that Tobirama Senju and Orochimaru were the only ones who knew how to use this technique, and Kabuto now claims to have mastered it to a degree even higher than them. Before the technique can be performed, a living sacrifice must be found. The sacrifice's body is used as a vessel for the soul of whoever is being revived, with dirt and ash encasing them to resemble the original body of the person being resurrected. The end product is stored in a casket until summoned by the user.

When first summoned, the body of the resurrected appears gray and in in a state of minor decay. They retain any memories and abilities they had in life, including kekkei genkai. At this point the revived still have their free will, and thus are not under the user's control. With the application of a special fuda tag their free will is removed, but their appearance is restored to a closer likeness of how they looked in life. This technique can be used to summon multiple people at once, depending on the amount of sacrifices and the chakra level of the user.

The revived are impossible to kill by normal means. If a limb is destroyed or removed, it will simply regenerate. To kill the revived, the soul has to be removed. Once this is accomplished, the bodies turn back to ash and dust, with the bodies of the individuals sacrificed lying among the ashes.

When Orochimaru used this jutsu, he sacrificed Kin Tsuchi and Zaku Abumi to revive Hashirama Senju and Tobirama Senju. Kabuto used it to resurrect Itachi Uchiha, Sasori, Deidara, Kakuzu, and Nagato simultaneously. He also summoned a sixth coffin with an unseen person in it, whose presence forced Madara to accept Kabuto's offer for an alliance.

Trivia

 * When Orochimaru used this jutsu against Hiruzen, three coffins were summoned, but Hiruzen stopped one of them. This third coffin is not seen in the manga, but in the anime it has written on it.