Limited

The Replibrain Limited (リミテッド) is a parasetic, semi-organic substance created by Dr. Doppler. It can evolve the capabilities of any Reploid or machine it is infused with, and uses the host as its own body.

Characteristics
Limited's core or "nucleus" resembles a light purple mechanical face with red evil eyes with a curved triangular design under them. It has a crystal above the eyes, much like the kind on Reploids, and two holes on either side of its "forehead". It has two tubes with an encased green bead-like structure leading from the sides of its head to underneath it. It is covered with an organic slime-like substance which acts as the catalyst for it's mutative properties. As a parasite, the Limited is capable of jumping from host to host even after its current host body has expired, with only the smallest physical contact needed to infect a Reploid. Due to its mutagenic and regenerative properties, the Limited is theortically indestructable.

Rockman X Mega Mission
Limited first appears in the third card of the Rockman X Mega Mission series, accompanied by Doppler. It is a device created by him which can control whatever Reploid it is fused with and evolve its body and abilities. X first encounters it when fighting Wire Sponge L, a revived Maverick infused and evolved with Limited. During the fight, the Limited within the revived Maverick fears for its survival and abandons Sponge's body, attempting to infiltrate X. Zero destroys the core with a buster shot, but the mutagenic slime-like substance still splatters onto X, causing his buster to mutate, forming the Clear Buster. X then fights more Revived Limited Reploids from Mega Man X and Mega Man X2, interrupted various times by Doppler's Incept Chaser Curtiss, seemingly interfering only when the Limited's core is in danger of being destroyed. Eventually attacking X himself, under orders to obtain his Limited fused Buster. He is defeated, and killed by his partner Schmitt when he is interrogated by X and begins to reveal information.

X and Zero fight and defeat more Limited Reploids, but now, the Limited appears to flee the body on its own upon defeat, indicating that the Limited itself was evolving. Eventually they are confronted by Schmitt, and during the battle, X's buster begins to mutate again, leaving X immobile and vulnerable. Zero takes his place, but a dirty move by Schmitt forces Zero to take a blow for X, leaving him injured. X's Buster finishes it's transformation just in time however, leaving him with the High Clear Buster. X defeats Schmitt, who retreats in to the Mother Limited to be repaired, but the Mother Limited instead swallows him up entirely and uses the accumulated data on X to turn him into "X", a Limited based doppelganger of Mega Man X. The Copy initially outmatches X, but the Limited in his body mutates again, this time mutating X's body, creating the Clear Armor and taking over X's body. The duo fight, but "X" is destroyed when both shoot final charge shots at each other's chests, destroying the clone, while X manages to use his double's attack to destroy the armor and move out of the way before it destroys him as well. From there, the Mother Limited transforms into a giant battle form to fight X and Zero. but the Hunters combine their power and both attack Mother Limited with Charge shots, destroying it, and escaping the area before it is destroyed by its explosion.

Rockman X Mega Mission 2: Versus Revenge Limited
In the prologue, we learn that Limited has the ability to regenerate itself as long as there is a single cell of it left alive, and thus Mother Limited narrowly avoided it's death at the hands of X and Zero, and evolved into a mysterious entity known as "Tackione". He and two other Reploids calling themselves "Order Breakers" then revived 8 more Reploids with Limited, evolving their bodies and abilities further. X is sent to investigate a town where the entire population has turned Maverick. Once there, he is attacked by Overdrive Ostrich-L, who he defeats by equipping his past weapon data on Crystal Hunter. Afterwards, he fights and defeats two more Limited revived Reploids, and encounters Chill Penguin-L. During this fight, X learns that Tackione and his cohorts have placed a Limited field over the town, which turns any Reploids under it into Mavericks. However it has also influenced the residual Limited still remaining in X's body, allowing him to use his previous special weapons much like he did in the first Mega Mission. After defeating Penguin, the exhausted X is confronted directly by the trio of Order Breakers, who overwhelm and kidnap him.

Meanwhile, Zero defeats the remaining four Limited Reploids, (as well as equipping the wreckage of X's buster left behind from his battle with the order Breakers and receiving the Energy Armor from Dr. Light) and confronts the Order Breakers. He fights and defeats Bloodione and Luxione, both of whom are actually pieces of Tackione that separated and matured. However, Tackione then reveals his newly acquired secret weapon to Zero- and X appears behind him, eyes blank, wearing the Replicapture armor, which is actually a large Limited parasite attached to X's chest, allowing Tackione complete control over X's body and mind. Zero battles X and wins, destroying the Replicapture Armor, but is critically damaged himself. Tackione himself then faces the duo, revealing that he is in fact the residual data of Doppler revived through Mother Limited, effectively making him "Doppler Limited". He attacks them and they manage to avoid his barrage, X even managing to wrestle Tackione's saber away from him. From there, Tackione evolves into a giant form similar to Mother Limited, but is eventually defeated by X using the Giga Armor's (The Neo Armor transferred to him from Zero) Giga Crash ability.

Trivia

 * Mother Limited's final battle form is very similar to the Devil type robots.
 * The Limited's characteristics are largely incorporated into the body of "X's" second form, with his chestplate itself modeled after its design.