Extremis

"A lot's happened, Tony, but I'm close. Extremis is practically stable." "I'm telling you it isn't! I'm on the street, people are going 'bang', they're painting the walls. Maya, you're kidding yourself." "Then help me fix it."

- Maya Hansen and Tony Stark

Extremis is a serum which allows the human body to instantly regenerate damaged tissue, including the immediate regrowth of severed limbs.

Creation
Extremis was created by Maya Hansen in 1999. Maya and Aldrich Killian upgraded it thanks to Advanced Idea Mechanics providing funding for it to begin experimental testing. A.I.M. recruited amputees and other disabled people as test subjects, most notably the victims of military ops. Extremis cured their disabilities after which they were convinced to work for A.I.M. as assassins and soldiers. Near the end most if not all of the Extremis Soldiers were killed by the combined forces of Tony Stark, James Rhodes, and J.A.R.V.I.S..

Extremis is also used in combination with several other substances by the clandestine organization Centipede, which is trying to create super soldiers. It is uncertain if Centipede is conducting its experiments before or after the events involving Tony Stark and Aldrich Killian occur.

Users

 * Aldrich Killian
 * Eric Savin
 * Ellen Brandt
 * Jack Taggart
 * Chad Davis
 * Virginia Potts (unwillingly and stabilised)
 * Michael Peterson (through Centipede)
 * Chan Ho Yin (through Centipede)
 * Brian Hayward (through Centipede)

Abilities
After Extremis is injected into the user's body, it enhances the user's physiology by rewriting their DNA. If the user's body chooses to accept it, the user will gain regenerative healing, making them able to heal all wounds, including previously amputated limbs or even psychological damage. When regenerating body parts, the wounds take on the appearance of burning ashes while growing back the lost body part, in a matter of minutes, and cooling into regular skin, flesh, and bone. Extremis also enhances physical performance granting superhuman strength, reflexes, and endurance.

Additionally, normal Extremis users gain the ability to generate extreme amounts of heat through a complex metabolic process, generating heat from their bodies up to several thousand degrees Celsius. Extremis users are able to consciously control the amount of heat expelled from their body, causing the area of their body generating heat to glow intensely. Trained Extremis users can focus and conduct heat through a single area of their body such as their arms or hands. Certain users also demonstrated the ability to conduct heat through other objects through physical contact, most often through large metal structures to cause them to weaken and begin to melt.

Through a combination of superhuman strength and a focus of extreme heat conduction through their arms and hands, Extremis users can strike through and destroy a majority of metal structures on contact. Due to this they are able to overpower the metal alloys that are used in most Iron Man armors, easily destroying many of the suits in combat.

Weaknesses
Extremis personnel can be easily recognized through thermal imaging as they have a much higher heat signature. They can also be identified as their pupils glow when using their powers. Extremis does not make its users entirely invincible, as wounds like a unibeam shot through the chest will be lethal, destroying the victim's heart and therefore cutting off blood flow to the brain. When the body is regenerating, it is fragile and can be destroyed with a repulsor shot.

The main weakness of Extremis is the possibility that its user’s body will reject the serum upon initial injection, or that the serum may become unstable within the user if they fail to regulate their usage of it properly. If either of these events happens it will cause the metabolic process that causes the user’s to generate heat to overload, causing the user’s body to explode. The resulting explosion is an excess of 3,000°C and completely incinerates the Extremis user’s body, along with anything within a certain proximity of the explosion. Due to this Advanced Idea Mechanics had to fake several terrorists’ attacks on United States' soil to cover up the explosions caused by Extremis test subjects.