Life Energy is the very energy of living organisms. It is never explained what exactly Life Energy is other than the fact it is life itself.
Throughout the Sonic the Hedgehog series games, Dr. Eggman's models of robots were powered by life energy. They were known as Badniks and were powered by small animals which trapped the animals inside themselves while all the while drawing energy from them to stay active. However a hit from the character could easily destroy them entirely harmlessly freeing the hostage within them.
Minus some exceptions in certain Sonic games, this method of powering Eggman's robots continued up until the game Sonic Heroes, as Eggman's new Egg Pawn robot line did not release any captured animals when released, suggesting they were powered through other means. However certain games, such as Sonic Rush still had animals trapped inside Eggman's robots.
In Sonic Lost World, Dr. Eggman restarts his Badnik series, which, as before, is powered by living animals, and shows the process of how the animals are "robotized" into Badniks (simply taken out of the capsule and drop inside a vacant Badnik). Dr. Eggman also constructs a machine known as the Extractor which, like his badniks with single little animals, is able to draw the life energy of the world itself and condense it into a green liquid state that can be consumed by robots and organic creatures alike to increase their own strength, as it is the same form of energy that powers Badniks only in liquid state. The machine however was made only to siphon off small, harmless amounts of energy from the planet. However, the Deadly Six eventually took over the control of the Extractor to extract all the life energy from the world, growing more powerful over time. After Sonic defeated the Deadly Six and Dr. Eggman, Tails manages to reprogram the Extractor to return the stolen energy back into the planet, restoring natural life.
In other media
During Series 2 (Season 3) of the anime series, Sonic X, a villainous group of aliens known as the Metarex sought after Planet Eggs, which are said to be the life force of each planet of the universe. Without it, the planet will eventually "die" which can happen in many ways depending on the planet.
- Life Energy could consist of various organic energy such as bioelectricity, body heat or based on various esoteric energy philosophies such as Qi, Mana or Vitalism.
- In the British comic Sonic the Comic, the victims that powered Dr. Robotniks badniks were recognised as organic batteries. The vacant badniks could be active but at limited capabilities until it takes in a victim. Sonic had to be careful fighting Badniks due to them holding a hostage.
- Life Energy can be compared to Ki from the DragonBall series. All life in the series possess some degree of the energy which, to those who know how to manipulate there own, can use it in powerful attacks or contribute it to other powerful attacks like the Spirit Bomb. However, unlike the DragonBall series, Life Energy is regarded just for living while Chaos Powers can be more comparable to the kind of techniques seen in the DragonBall series.
- The world life energy can be compared to the Lifestream from Final Fantasy VII in which it is the essence of life of Gaia itself which can be extracted in a green liquid energy state known as Mako energy.