Weapon Copy System

The Weapon Copy System is a feature that allows the user to copy a Special Weapon from a Robot Master or a Reploid. It was originally Mega Man's signature ability, but it has been used by other robots since. It is also known as the Variable Weapon System.

Characteristics
The user's armor changes colors to match the special weapon in use. The copied version is usually similar to the original, although it is often less powerful in comparison. Each copied weapon has a limited stock of Weapon Energy, and the amount consumed with each shot tends to be proportional to the weapon's power.

The copied weapon is not lost if its meter is depleted, but it must be refilled before it can be used again. Weapon Energy items can partially refill the bar (normally, the weapon must be equipped for this, but the Energy Balancer eliminates this necessity). W-Tanks refill one weapon's bar completely, while S-Tanks refill all weapons.

Despite its limitations, the sheer versatility of the Weapon Copy System makes it a very powerful and threatening ability: a user clever enough to copy the appropriate weapon can target the next opponent's exact weakness, providing a major advantage in battle. Using a copied weapon does not change the user's natural weaknesses.

Save for rare exceptions, most copied weapons cannot be charged like the Mega Buster. X is the first to show the ability to charge his copied weapons, although this requires one of Dr. Light's buster upgrades.

The actual process of copying a weapon seems to vary. In a journey to stop Ra Moon, Mega Man obtains his weapons by taking chips from other Robot Masters. X's system copies a weapon by taking the DNA data of his opponent.

Mega Man series
Mega Man is the first user of the Weapon Copy System, which he has used proficiently to stop Dr. Wily's multiple campaigns for world domination. Bass, the robot created by Dr. Wily specifically to defeat Mega Man, Bass was later revealed to have a Weapon Copy System, but he ironically never used it against Mega Man himself. In certain occasions, Proto Man and Duo also demonstrated use of the Weapon Copy System.

Mega Man X series
Dr. Light's final creation, Mega Man X, is the only known user of the original Weapon Copy System (called Variable Weapon System in his specifications). However, Zero has a similar feature known as his Learning Ability, which allows him to acquire new skills and techniques from his defeated opponents. Axl and the New Generation Reploids have an arguably more advanced ability brought by their copy chips, which can copy the actual forms of other Reploids.

The original Weapon Copy System technology seems to have been lost with time, since no one after X has demonstrated this ability; though it's entirely possible that, seeing as its intended purpose is for combat, Dr. Cain simply didn't see fit to install a Weapon Copy System in the average Reploid.

Marvel vs. Capcom: Clash of Super Heroes
Mega Man and Roll both have a special move called Weapon Change, where Rush provides a special weapon module for their use. The weapons available are the Mega Ball, Tornado Hold and Leaf Shield.

In Mega Man's ending, he copies Onslaught's Magnetic Shockwave attack. In the PS version, it becomes one of Mega Man's hyper combos after clearing the game.

Mega Man (animated series)
Mega Man often copies at least one weapon during a climatic battle to solve an immediate crisis. His most prominent use of Weapon Copy occurs when Dr. Wily terrorizes the seas: Mega Man stops this scheme by copying the weapons of every Robot Master onboard Dr. Wily's "floating fortress of doom", including Proto Man's, in order to build up enough plasma energy to overload the engines. He also makes a creative use of his ability to copy the schematics of an energy-draining web on Dr. Light's request.

Although Proto Man also has this ability, he only uses it once to copy Guts Man's Super Arm.

Later on, a time traveling Mega Man X copies the Search Snake to destroy a laser cannon built by Dr. Wily with aid from Vile and Spark Mandrill. As a more advanced model, X's version turns out to be much more powerful than the original, as a single shot ravages the cannon in a matter of seconds.

Notes and Trivia

 * Neither Mega Man nor Proto Man change colors when using the Weapon Copy System in the cartoon. Mega Man and Roll do not change colors in Marvel vs. Capcom either, perhaps to avoid confusion with their alternate colors. Mega Man also does not change colors when using other weapons in Super Smash Bros. for Nintendo 3DS / Wii U, although his alternate color palettes represent the weapons present in his moveset.
 * X does not use his Variable Weapon System in Mega Man X: Command Mission, although he can equip elemental variants of the X-Buster for similar effect, and one or two boss NPCs show some awareness of X's copy-ability.
 * Duo is the only user of the Weapon Copy System whose primary weapon is not a buster, though in the arcade games Duo's fist functions more or less in the fashion of a buster.
 * In some games such as Mega Man X8, it is possible to use the standard buster and a copied weapon simultaneously, generally when the controller has enough buttons to accommodate the feature.
 * The Magnet Beam and the Mega Ball are the only weapons which are not obtained via the Weapon Copy System.
 * The concept of MegaMan.EXE's Soul Unison seems to be based on the Weapon Copy System.