Blood bending

Psychic bloodbending

A restrained Yakone effortlessly bloodbending Chief Toph Beifong.

Psychic bloodbending is the ability to use bloodbending without the aid of motion and movement of the hands or feet. Yakone first demonstrated this ability when he used bloodbending to control an entire courtroom while his hands were still bound by cuffs. He passed on the knowledge of this technique to his sons, Noatak and Tarrlok. However, only Noatak mastered the ability, doing so at the age of fourteen and able to control an entire pack of wild animals at once.

Bending severing 

Lightning Bolt Zolt losing his bending.

Bloodbending can be used to completely cut off a bender from his or her bending abilities. This technique has only been demonstrated by Amon and requires direct physical contact between the user's hand and the victim's forehead. The effects of this technique are long-standing, and, unlike chi blocking, it cannot be easily undone. According to Katara, the technique "severs" an individual from his or her bending, making it impervious to all methods of healing. Even so, only active chi pathways can be severed; Korra was able to use airbending because it was still dormant when her other bending abilities were removed. However, the severed bending can be restored through the use of energybending, as shown by Aang and Korra.<sup>[6]

Bloodbending is the only known way besides energybending to strip a person of their bending indefinitely. 

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Some explanations when Aang bends Ozai

The lion turtle was seen again in a flashback, right before Aang began energybending Ozai, where he spoke the words: "In the era before the Avatar, we bent not the elements but the energy within ourselves..." Aang, with these words in mind, began to bend Ozai's energy. The final time the lion turtle was heard, he spoke the words: "To bend another's energy, your own spirit must be unbendable or you will be corrupted and destroyed..." During this time, Aang's energy managed to overpower Ozai's and he succeeded in taking away his ability to bend.^[5]

TRIVIA: 
Nyla was unable to find Aang while he was on the lion turtle due to the fact that the lion turtle had traveled all over the world for so long, accumulating countless new smells, that it smelled like the earth itself, thus masking Aang's scent.

^SOUCE 

LION TURTLE's QUOTE

"The true mind can weather all the lies and illusions without being lost. The true heart can tough the poison of hatred without being harmed. Since beginning-less time, darkness thrives in the void but always yields to purifying light."

— The lion turtle sharing his wisdom with Aang in "Sozin's Comet, Part 2: The Old Masters".

CHAKRA