Green Energy is the provisory name given to the energy released when the strange green matter is burned. The green matter is present on Saturn's arms in the form of dense crystals and apparently in the body of the Mysterious Man.
Saturn always shows up with a massive amount of green matter on his arms, which has a percentage of its material vaporized every time he casts an attack. The actions performed by the green matter are apparently determined by orders given by its user, hand signals in his case, as if the green matter was composed of entities that could understand his will or were somehow programmed to react to the signals that cannot be cancelled once sent. The commands vary from the green matter igniting itself to a vortex that carries its surroundings to another point of the space like a wormhole, and wasting a huge amount of green matter in the process according to the mass and duration of the vortex.
In Prologue: Doomsday, Saturn spent half of his green matter to teleport himself, Shad and Gigantex to the 17th Elite Unit and make a surprise attack, while normal teleports couldn't be performed due to the intense jamming. Saturn didn't fight X and Zero with the excuse that he would spend the remaining energy that would be used to bring Gigantex back, and if he did that more of their friends would die.Ineluctable Demise, it was shown that Saturn's body is actually a shell that hides a green matter crystal body and the particles can mold themselves in very defined shapes without his consent, as if something or someone was controlling their behavior meticulously. Later, when Saturn called for help from an unknown entity, although it seemed like he was talking alone, the crystal blade that took over his destroyed arm transformed into a new hand to form the Gate signal and open a giant vortex to capture the encorium ore from Dr. Henry Snacman's laboratory.