Sage Mode

Sage Mode is the result of using natural energy along with a shinobi's normal chakra to drastically empower all of their abilities.

Overview
Sage Mode is the empowered state humans enter when they learn to draw natural energy inside them and blending it with their chakra. By doing so, the human creates new senjutsu chakra that allows them to enter Sage Mode. The physical benefits of Sage Mode depends on whom the human learned under but generally Sage Mode enhances the combat efficiency of the user by allowing them to tap into the natural force of the world that opens new techniques to the user and allows them to power existing ones with senjutsu chakra.

Training
According to Fukasaku, only those who already possess "extreme chakra levels" can utilise natural energy to invoke senjutsu. Also, the users body most be strong enough to support Sage Mode; Orochimaru learned senjutsu but was unable to use Sage Mode because his host body was not strong enough to support power, and he didn't have the chakra levels to utilize the natural energy. Because of this, he created his Cursed Seals using Jugo's Sage Transformation enzyme to work around it.

The user is required to balance his/her physical and spiritual energy with the natural energy he/she gathers from nature; Gamakichi compares the process to adding an extra flavour to a chocolate and vanilla swirl ice cream. If the user puts too little natural energy into using senjutsu, the technique will not work.

The method of learning the other styles of Sage Mode are unknown, as the only one shown was the toad style. For the toad style of Sage Mode the gatherer must remain absolutely still in order to be one with nature. Those learning from the toads can use a special toad oil that allows the natural energy to enter their body, but this oil only exists in liquid form in Mount Myōboku's atmosphere. The oil evaporates if it is taken outside, thus rendering it useful only for learning purposes. If the user takes in too much natural energy, the user will start to turn into a toad and, eventually, turn to stone. The petrified remains of one-time apprentice Sages who failed to master senjutsu are spread throughout Mount Myōboku.

Getting hit by a special staff during the transformation will reverse the toad transformation by knocking all the natural energy out of the gatherer. It is dangerous to learn how to gather natural energy without the staff because there is no other known way to reverse the toad transformation. Furthermore, if the transformation is completed, not even the staff can reverse it, and the user would become a toad statue forever.

Advantages
Taught and learned by the toads, the advantages afforded to those who study senjutsu from the toads include:
 * The user's physical strength, speed, stamina, reflexes, perception and durability dramatically increase.
 * The user's ninjutsu, genjutsu, and taijutsu become more powerful.
 * The user can harness the natural energy surrounding them, turning it into an extension of their body, which increases the reach of their attacks.
 * The user gains the ability to sense chakra around them.

Disadvantages
There are a few disadvantages while using this mode as well, these include:
 * If the user draws in too much natural energy, they run the risk of transforming into a toad, then into stone. If the petrification is completed, it cannot be reversed.
 * In order to gather enough natural energy to initiate the transformation into Sage Mode, the user must remain perfectly still. Because of that, the user can be an easy target for an opponent.
 * Because the user needs to move during combat, the senjutsu chakra cannot be replenished, which means the user can't stay within this state for extended periods of time.
 * The second and third weaknesses mentioned above can be bypassed through the Sage Art: Amphibian Technique, where one Sage gathers chakra for another or as in Naruto's case, shadow clones can be used for the same purpose.
 * After Sage Mode has ended, the user appears to experience exhaustion.

Imperfect Toad Sage Mode
Jiraiya was not able to completely balance his own chakra with natural energy, resulting in him using an imperfect form of Sage Mode. As a result of the imbalance (and the imperfect nature of his transformation), Jiraiya took a number of toad-like traits when using Sage Mode (such as his big hands or his skin). His appearance was altered: his nose grows bigger and gains warts, he gains excess hair (his goatee), and toad-like eyes. Further transformational attributes includes him taking on a toad-like stature and the lines on his face become much thicker, taking over each side of his face. Because of these traits, Jiraiya didn't like to use Sage Mode as it "displeased the ladies". He also showed the ability to transform his limbs (e.g. his hands and feet) into those of frogs so as to aid in manoeuvrability.

In order to get around the danger of remaining stationary during a battle to re-enter Sage Mode, Jiraiya would summon Shima and Fukasaku by drawing a blood contract on his face. The Two Great Sage Toads would fuse to Jiraiya's shoulders with the Sage Art: Amphibian Technique, gathering natural energy from their stationary positions on Jiraiya's shoulders for him to use.

Perfect Toad Sage Mode
Unlike Jiraiya, Naruto Uzumaki is able to perfectly balance the natural energy with his own chakra. This allows him to use Sage Mode in perfect balance, which allows him to retain all of his normal physical characteristics except for toad-like eyes: yellow irides, horizontal bar-like pupils, and reddish-orange pigmentation around the eyes; the mark of a true sage on each eye. A true sage would still suffer from the weaknesses of Sage Mode, requiring that they use Sage Art: Amphibian Technique in a battle situation. Because of the animosity of the Nine-Tailed Demon Fox sealed within Naruto, however, Fukasaku was rejected whenever he tried to fuse with him.

As a workaround, Naruto has some of his shadow clones gather natural energy elsewhere while he fights. Once he has run out of his own senjutsu chakra, he reverse summons the clone and has them disperse, giving him the clone's natural energy and allowing him to enter Sage Mode again. This method limits the maximum number of shadow clones that Naruto can create to five for as long as the clones are gathering natural energy, as anything more would interfere with their focus. To make sure he has enough shadow clones for use in battle, Naruto has only two shadow clones gather senjutsu chakra, allowing him to enter Sage Mode a total of three times. Naruto has also stated that it is possible to lengthen the time he is in Sage Mode. Naruto's skill in senjutsu has increased to the point that it doesn't take him nearly as long to enter Sage Mode.

Tailed Beast Influence
During his meeting with Nagato, Naruto was stabbed in the stomach with one of Nagato's chakra receivers. Nagato noted from that distance he would have been able to easily control the jinchūriki. However, while the young man was in Sage Mode, the fox's rage also spilled over into the form, and was reflected by Kurama's eyes being reflected in those of Naruto's Sage Mode: the irides turn red, and his pupil resembles that of both the fox's and his own when in Sage Mode, reminiscent of a cross. Some time later during Naruto's battle against the Ten-Tails' jinchūriki Obito Uchiha, Naruto once again used these two powers to create powerful attacks bolstered by the natural energy from Sage Mode even going as far as to mix natural energy with the Tailed Beast Ball. In this form, Naruto's eyes take on the same appearance as before. The markings of the Sage are also reflected on Kurama's Tailed Beast Mode shroud.

Advantages
Senjutsu which can also be studied from the snakes of the Ryūchi Cave also gain a number of advantages while using Sage Mode in battle, these include:
 * The user's perception abilities, reflexes, strength, speed, and stamina dramatically increase.
 * The user's ninjutsu, genjutsu and taijutsu becomes more powerful.
 * The user gains further access to snake anatomy, such as their brille, which can be used to lock out light as well as stop visual-based genjutsu from affecting them. They are also able to perform abilities that are characteristic of snakes, such as dislocating their jaw, although this is not exclusive to this mode.

Disadvantages
While mobile, the user is rendered incapable of gathering natural energy while remaining still in battle would leave them open to attack. However, Kabuto Yakushi assimilated the DNA of Jūgo to replicate his clan's ability to passively absorb natural energy, thus allowing him to continuously collect the energy even while moving, bypassing this one weakness and metaphorically proclaimed that he transcended from snake to dragon.

Forms
While retaining most of his normal physical characteristics in Sage Mode, Kabuto Yakushi did display greater areas of darkened pigmentation of the markings around his eyes which tapered off after reaching his shoulder blades. More noticeably, he gained four horns growing out from the back of his head as well as darkened sclerae.

Advantages
In this mode Hashirama's abilities were drastically increased. This was witnessed through the use of his Sage Art: Wood Release: True Several Thousand Hands technique which created a gargantuan multi-handed structure which easily dwarfed several mountain ranges as well as Kurama. Hashirama can also perform Sage Art: Gate of the Great God, a technique that can bind a creature as powerful as the Ten-Tails.

Disadvantages
The user has the disadvantage of having to stay still for a certain amount of time so they can gather enough natural energy to form the special senjutsu chakra. Thus, the user is left vulnerable while doing this. Unlike Toad Sage Mode, this version of Sage Mode doesn't carry over to any clones, which are created in base form.

Forms
In this mode, he retains all of his normal physical characteristics. He gains, however, a red pigmentation around his eyes, and his face gains several markings inclusive of a circular one in the middle of his forehead.

Trivia

 * In the film Naruto 5: Blood Prison, the red coat Naruto wore during his return in the Invasion of Pain would appear when he enters Sage Mode. Like every other physical change with the form, it would disappear when he turns back to normal.
 * The manifestation of animal like traits through the activation of natural energy and the performance of senjutsu, is a reference to the Jiraiya Ninja folk tale, where Jiraiya, Tsunade, and Orochimaru came to study specific animal magic into their ninjutsu use.