Force Metal

Force Metal is a material first talked about in Mega Man X: Command Mission and is a large premise in the plot. Extraterrestrial in origin, its discovery and usage eventually lead to the creation of Giga City. It has the side-effect of causing Maverick-like symptoms in Reploids who overuse it, with Prof. Gaudile mentioning that the release of the Supra-Force Metal energy from the missile would create "a mass of Mavericks" over a half of the planet.

It is a material that can alter the abilities of Reploids that use it, such as increased WE gain, more health, resistance to certain elements and so forth. In Command Mission, it is used as a form of equipment, similar to accessories from other RPGs. Each Reploid only has a certain number of Force Metals. X, Axl and Spider can equip the most at four while Massimo can only handle two; the rest can equip three.

Each character has a Force Metal Erosion stat that increases when they level up. The stat varies greatly between characters with Cinnamon having the most and Zero with the least. As long as the combined Erosion rating of the equipped Force Metals equals or is less than the character's Erosion stat, everything is fine. Going over the amount causes Force Metal Hazard, resulting in massive LE or WE Gain cuts in battle, which only become more severe the more the Erosion rating is gone over.

One type of Force Metal, Supra-Force Metal, has 10,000 times the normal Force Metal energy, requiring "a ton" of Force Metal to make. The specifics of what it does exactly are never gone into, but it seems to basically super-power everything about the Reploid who equips it, as evident by the fragments and the remarks by the villains. While only used by the bad guys, it's possible to steal fragments of Supra-Force Metal from the final boss to use in the post-game. They are the only Force Metals to have the maximum Erosion rating of 99 and require Erosion reducing equipment to use.

Supra-Force Metal plays the largest role in the plot and serves as the primary motivation for both sides after Chapter 7, with the Rebellion attempting to use it to prepare a missile warhead armed with it and X's team trying to stop them. Only two samples of Supra-Force Metal are seen, one as the initial warhead payload and the other used by Epsilon. Eventually, Redips acquires both samples for himself to build his Great Redips body and begin his attempt at universal conquest. After his defeat, they are destroyed by Ferham's self-destruct.

Trivia
A substance simply called Metals appear in Mega Man X8, but bear no relation to Force Metal as it had not yet be discovered at this point in the timeline.