Outer Path

King of Hell a technique, used by the Naraka path, that summons a giant demonic figure with the apparent use of interrogation. It is capable of discerning whether an individual is lying or not. When implemented on a target, a serpent-like apparition emerges from their mouth and it is consumed by the figure. If they are lying (or refuse to answer the question), their life force energy is taken and they die. If the target is telling the truth, they don't die, though they're left extremely exhausted. When the Naraka path uses this technique, the figure possesses the Rinnegan eyes similar to how the Animal path's summons all possess the Rinnegan. The King of Hell can only be seen by the ones it's being used upon.

As a secondary ability, the King of Hell can re-infuse new life force energy to the dead body it eats. When it consumed the remains of the Asura path, the Path emerged from the figure fully restored and is even wearing new Akatsuki robe (the body had discarded its previous robe). Once Naraka path uses this technique, he needs time to recharge and possibly cannot use King of Hell at all. While the King of Hell is being used for revival purposes, it seems that others are able to see it, unlike when it is being used for interrogation purpose. However, it was Naruto in Sage Mode that was able to see it, so it is possible that normal people cannot, even for revival.

The King of Hell can be summoned when the Outer Path: Samsara of Heavenly Life Technique is used, where Nagato can release life force energy to people who were recently killed, allowing their souls to return to their rejuvenated bodies.

Trivia

 * This technique is likely based on the Japanese folk proverb that the god of hell will rip out your tongue if you lie, a tale told to children to scare them into telling the truth.