Six Paths Senjutsu

The Six Paths Sage Technique is an empowered state, similar to Sage Mode, which drastically empowers all of the user's abilities to a far greater extent by either having the Ten-Tails's chakra or combining senjutsu and the chakra of all nine tailed beasts.

Naruto's Version
While using this power, Naruto's Sage Mode takes on a similar appearance to it's Nine-Tails chakra-enhanced variant. His eyes are yellow as opposed to orange or red, and there is no orange pigmentation around his eyes that a normal Sage Mode would entail. In this state, Naruto can utilise Yang Release to rekindle Might Guy's extinguishing chakra after the latter had used the Eight Gates Released Formation, as well as restore Kakashi's original left eye after Madara stole his Sharingan. Naruto's physical abilities were also bolstered to the point where he was able to overwhelm Madara in his Ten-Tails jinchūriki form, forcing him to absorb the entirety of the Ten-Tails' tree form.

Naruto can extend the capabilities of the form by further drawing on the chakra of the nine tailed beasts, causing him to don a chakra cloak which is noticeably more powerful than the Nine-Tails Chakra Mode. In this mode, the chakra forms into a light-coloured coat with a dark-coloured bodysuit underneath. The "bodysuit" covers his torso, reaches down his arms to the knuckles, and down his legs, stopping just above his sandals. It has a light coloured circle where his seal was placed as well as magatama markings around his collar. The coat has the typical markings of the Six Paths Sage Technique; a Rinnegan above nine magatama, on its back. In this state, Naruto is able to manifest the Truth-Seeking Balls, wielding two of them as short staffs. His speed is immensely increased. Like the previous transformations, Naruto can form chakra arms. He also gains the ability to fly.

Obito and Madara's Version
Madara has stated that both he and Obito both possessed this technique upon becoming the Ten-Tails jinchūriki. Obito achieved two forms of the Six Paths Sage Technique; the first which he achieved in his initial form. In that his body became scaly, he got the Rinnegan symbol and the nine tomoe on his back, and he possessed only two Truth-Seeking Balls which were attached to his hands. After gaining control over the Ten-Tails, he possessed a chakra cloak behind him, gained small horns on his head with one over his Sharingan being bigger than the one over his Rinnegan and his Truth-Seeking Balls increased to ten. Madara also underwent similar transformations. His skin became grey and his hair turned taupe-colour. Instead of possessing clothing-like flesh, Madara was instead cloaked with a complete outfit composed of chakra, with a pattern of six magatama below his neck and a pattern similar to Hagoromo's on his back. He also gained a forehead protector-like horn which emerged from the left side of his forehead, and had an upward curve on its right side and a single horn on its left side. He was able to create ten Truth-Seeking Balls, one of which formed the other half of Hagoromo's shakujō.

As the jinchūriki of the Ten-Tails, both gained immense increases in their physical capabilities and were able to completely overwhelm their powerful adversaries. Even when Obito initially had no control over himself, he was able to destroy the Hokage's barrier as well as Hashirama Senju's gates with ease, as well as overwhelm all four reincarnated Hokage. This power amplified greatly upon having complete control of the Ten-Tails.

Despite both Madara and Obito gaining enormous increases in power, Minato Namikaze noted that Madara's power in this form is greater than Obito's. With it, Madara was able to fight on par against Guy using all Eight Gates and survive the latter's final attack. His speed was also greatly increased, able to counter a combination of individually fast techniques. Madara's regenerative powers and durability are also greatly enhanced, able to survive the left side of his torso being obliterated or being bisected and soon after completely restore himself. With his immense regenerative powers, Madara claimed he had achieved complete immortality.

Trivia

 * While not an actual user, during the Fourth Great Shinobi War, Obito transferred some of this power into Kakashi Hatake, allowing him to replicate certain feats including augmenting his technique's power.