Every type of sub-bending in Avatar: The Last Airbender

Fire:

1. Lightningbending

Labeled the "cold blooded fire" by Uncle Iroh, lightningbending is one of the most dangerous forms of sub-bending and can cause serious damage to anyone on the receiving end. In Avatar: The Last Airbender, only members of the Fire Nation royal family were capable of generating lightning, including Iroh, Azula and Ozai.

However, during The Legend of Korra, we see that lightningbenders are much more common, to the point where a power plant in Republic City employs dozens of them. Likewise, several characters in The Legend of Korra demonstrated the ability to redirect lightning, which involves guiding the energy through your stomach and out your other arm. Iroh developed this technique after studying waterbenders.

Lightning played a massive role in Avatar as Azula temporarily kills Aang with the power at the end of season 2. One of the main reasons Fire Lord Ozai was such a huge threat is because he was one of three people in the world who could actually use lightningbending, and he did so multiple times during his final fight with Aang. Luckily, Zuko taught Aang how to redirect lightning and he was able to gain control of the Avatar state again to defeat Ozai through different means.

2. Combustionbending

One of the rarest abilities on this list is combustionbending, which involves the user focusing all their energy into a powerful blast that shoots out of their forehead. The blast appears as a precise stream of energy that can be shot form a long distance and explodes upon impact. The only people who we see use this ability in either series are P'Li and the appropriately named Combustion Man.

Combustion Man was an assassin hired by Zuko to kill Aang. He encounters team Avatar on several occasions. Although the initial shock and awe of his attacks is daunting, combustionbending has drawbacks. When Toph earthbends a rock that strikes Combustion Man's forehead, his bending seemed to backfire and explode instantly.

This is likely how Combustion Man lost his right arm and leg; at some point, hee didn't know how to control his bending, and learning was dangerous. Similarly, Sokka once struck Combustions Man's head with his boomerang, which caused a fatal backfire that presumably killed the assassin.

In The Legend of Korra, P'Li demonstrated the ability to curve her combustion shots. However, metalbending proved to be a great counter to combustionbending as Suyin encased P'Li's head with metal right as she was bending, causing her head to explode. Definitely one of the more brutal moments from this series but I loved it.