Limbo: Border Jail

Using his Rinnegan, Madara Uchiha projects a shadow of himself into, an invisible world that coexists with the physical world but that is ordinarily impossible to detect, perceive or even physically interact with. With one Rinnegan, Madara can form only one shadow, but with two Rinnegan, he can form up to four. Each shadow has the same abilities as the real Madara, with the added advantage of being untrackable. The shadows can attack targets, giving the appearance of an inexplicable force knocking them down, or they can defend Madara, giving the appearance of an invisible wall around him. A shadow's very formation can be used defensively, taking Madara's place mid-attack as a sort of Body Replacement Technique. After a certain amount of time, a shadow will need to return to Madara's body, and he will likewise need to wait a certain amount of time before he can reform it.

Against most opponents, Madara's shadows give him an insurmountable advantage. But Naruto Uzumaki and Sasuke Uchiha, after receiving Six Paths chakra, undermine some of the shadows' usual benefits: Sasuke can see them with his own Rinnegan; Naruto can sense them while using Six Paths Sage Mode; Naruto can damage them using Six Paths Senjutsu. Through a combination of these skills, Naruto is able to capture a shadow, preventing it from returning to Madara.

Madara prioritized keeping the mechanics of this technique a secret, as shown when Obito still had a Rinnegan, Madara decided it was best to avoid using this technique against him.

Trivia

 * Both the first word's furigana and the second word  refer to Limbo, with リンボ being the Japanese way of writing Limbo and 辺獄 being an actual translation of the word's meaning.
 * In Naruto Shippūden: Ultimate Ninja Storm 4, Madara's Limbo clones are capable of using Susanoo.