Specialized bending techniques

Within at least three of the four bending styles, there exist more advanced moves that only a master can take advantage of. It takes either years of practice, or a bending prodigy to be able to manipulate outside of a certain move pool.

Metalbending


Metalbending is a special subset of techniques within Earthbending that allows an Earthbender to ferrokinetically bend processed metals much as they would bend regular earth. It was developed by Toph Bei Fong while she was confined in a metal box. As of the end of the series, Toph remains the only known individual capable of Metalbending.

During a lecture on chakras, Guru Pathik explained to Aang that metal is merely earth that has been purified and refined. Using her unique ability to "see" through Earthbending, Toph is able to perceive the trace amount of earth still present in the metal, target it, and utilize it to "bend" the metal itself.

Seismic Sense


Seismic Sense is the ability to perceive objects' locations by feeling acute vibrations through the ground. Similar in application to sonar and echolocation, Seismic sense enables the practitioner to visualize earth-based objects or objects in contact with earth-based objects when out of sight or, in Toph's case, unable to be seen due to blindness. Only two known benders have been seen to possess Seismic Sense: Toph and Avatar Aang. Badgermoles, the primal Earthbenders, use Seismic Sense as an innate substitute for eyesight.

Waterbending
Water is the most versatile of the four bending elements. It is able to become any of the three states of matter: liquid, solid, or gas. Given these unique traits, there are several special abilities that a Waterbending master can learn.

Bloodbending


Bloodbending is introduced by the Southern Waterbender, Hama. Since the human body is roughly 70% water, Bloodbending does not necessarily bend blood, but the fluids in one's body, allowing the user to manipulate a body's muscles to move as they wish or to stop movement completely. Potentially, a Bloodbender could stop a victim's heart or crush his or her internal organs, pressurize, boil or cool the fluids, or even completely extract the fluids from one's body imitating the technique used with plants, though this has not been stated. Bloodbending can only be performed at night during the full moon. Only two people, Katara (albeit reluctantly) and Hama, have been shown to have mastered this technique.

Plantbending


A member of the Foggy Swamp Tribe, Huu, has illustrated that talented Waterbenders can manipulate plant life--from the highly water-saturated vines and roots found within the swamp lands and seaweed from the ocean floor--they can even rapidly regenerate the plant mass of the plants they bend (since the cell tissues of a plant is more versatile than the cell tissues of an animal), all by bending the ample amount of water within them just as they can with watery mud, as Hama demonstrated with fire lilies. Going further, a skilled Waterbender is able to separate and completely extract the water from plants for more effective utilization just as they are able to separate the water from mud, sand, and even polluted river systems, etc. In the case of plant life, this process will then leave behind the withered remains of all the affected plant life or even making them collapse in the case of large trees.

Healing
Waterbenders also have the unique ability to heal themselves and others. They do this by drawing on the life-giving properties of water to heal many types of physical wounds, some illnesses, and even pain caused by mental stress. There are limits to what can be healed. For example Katara's healing could not heal the organ damage done to Jet by Long Feng, Yue's birth illness could not be cured by human healers, and Zuko's scar would be unaffected by Healing (except for water from the spirit oasis). It is also apparent that Katara cannot heal a bender whose chi has been blocked as shown when she is unable to heal the Terra Team. Water from the Spirit Oasis, however, has special properties and can heal wounds that regular water could not such as Aang's near fatal lightning wounds obtained during a duel with Azula. It is possible that a healer can detect where chi flow is blocked. This is displayed when Katara can feel the energy locked within Aang's chakra during a healing session.

Lightning Generation


Lightning Generation is a sub-technique within Firebending, with which Firebenders are able to produce and direct a bolt of lightning from their fingertips. The generation of lightning was first shown by Princess Azula while she was being overseen by Lo and Li. Generating lightning involves a circular motion with the arms. Mentally, it involves a complete absence of emotion and peace of mind, and physically it requires separating the energies of yin and yang (the spiritual interpretation of positive and negative electric charge). When the forces collide, the bender only guides, rather than controls, the lightning's direction. Because of this complexity, a lightning attack usually takes much longer to initiate than standard fire attacks, however Ozai was shown generating lightning very quickly when he attacked Zuko.

Lightning Redirection
Lightning Redirection is a sub-technique within Firebending, allowing a Firebender to absorb lightning into their body as energy, then release the lightning in a more desirable direction. The technique was developed by Iroh after he studied master Waterbenders, who redirect force rather than oppose it head-on. Lightning redirection works equally well for natural and generated lightning. Iroh created this technique by watching Waterbenders, and taught it to Zuko, who in turn taught it to Aang. Zuko redirects lightning multiple times in the series, as does Iroh. Aang only uses this technique during his battle against Ozai.

Combustion


Combustion Man had a unique ability to channel his chi through his extremely overdeveloped third-eye in order to create a beam of energy by superheating the air around him. The beam explodes on contact, and is capable of great destruction, both in short and long range. Unlike normal Firebending, this does not produce a flame directly from the body. Good chi flow is essential for this technique to be effective, as disrupting it can have fatal consequences for the user, as shown when Sokka hit his eye with a boomerang. Despite superheating the air, it doesn't appear to harm its user, unless the explosion occurs in the immediate vicinity. It can instantaneously evaporate large bodies of water with ease. It is possible to counter fire attacks, such as when Combustion Man stopped Zuko's fire shield during their brief duel at the Western Air Temple.

Trivia

 * Airbending is the only bending art which as of the events of Avatar:The Last Airbender, does not have a specialized bending technique.
 * It has been hypothesised that amplification/soundbending exists as a sub-skill in Airbending. Aang used Airbending to amplify the range of his Bison Whistle to round up all of the escaped zoo animals. This, however, has not been confirmed to be a sub-skill.
 * All of Team Avatar's benders have displayed the ability to use more than one specialized technique. Some of said skills used were Healing, Bloodbending, Metalbending, Seismic Sense, Lightning Generation and Redirection.