Madrox's power is the ability to create duplicates of himself (sometimes at will) through an unknown process whenever he absorbs kinetic energy such as when he is struck, when he snaps his fingers, or stamps his foot. Each of the duplicates (dupes) is completely capable of independent thought and can create duplicates of himself. The original Madrox can absorb them back into himself at will, at the same time absorbing the memories, skills and experiences of the dupe. The dupe usually appears to his side or often near a focused area, such as a finger. Jamie wears special shock-absorbent suits that inhibit his dupes from manifesting inadvertently. Older versions of the suit covered Madrox's entire body, except for his face, and were dotted with small, circular shock-absorbent pads. Jamie currently wears a stylized shirt with only six large green shock-absorbent pads on the front of the torso. Whether this indicates a greater degree of control over when his dupes manifest or simply an advance in technology is unclear.
During his time with X-Factor, the maximum number of dupes Madrox could create (including the dupe's dupes) was about 40, but has grown far larger since then. Duplicates have independent minds from the original, but are usually willing to merge back because their memories and knowledge are retained. However, there have been exceptions where duplicates have wished for independence completely. A dupe that is "the part of you that can't be trusted" has announced that he plans to keep popping out.
As a last ditch effort, Madrox's abilities can be used to deadly effect, which were used in self-defense against Seamus Mellencamp in X-Factor #92 (July 1993), when Madrox jammed his hand into Mellencamp's mouth and activated his power, creating duplicates inside Mellencamp and exploding him from the inside out.
His powers have, at least once, been shown to affect the actual design of the shirt he was wearing.
Madrox also uses merging with his duplicates as a form of healing. Originally, uninjured dupes "shared" the damage when they merged, e.g., if an injured Madrox merged with an uninjured Madrox, the resulting Madrox had an injury half as severe as the original injury. Now, however, the core Madrox can reabsorb injured or even near-dead dupes without taking on any of their physical injuries at all, although the memories of traumatic experiences still affect him.
As a consequence of splitting into multiple selves, Jamie has accumulated a vast wealth of knowledge and experience, along with some confusion over which Jamie did what. For example, although he says his duplicates have had active sex lives, he is not sure whether the main Jamie ever has. Because of the infinite nature of his powers, his duplicates can potentially represent a variety of aspects of his character and to varying extents. One or two of his duplicates have already been shown to be gay or bisexual.
Specific special skills accumulated through his vast experience include picking locks, some proficiency in Shaolin kung fu, handgun training, multiple languages including Russian and Hawaiian, and playing-card throwing. Along the way, he and/or his duplicates participated in an Olympic gymnastics team and apparently became a licensed attorney.
The extent of how many 'dupes' Madrox can produce and how many are still at large is unknown — at one point, an upper limit of forty, counting the original, was established, but this has since been called into question. It is conceivable that he has dupes in the far corners of the world.
Madrox has generally been considered a mutant. However, unlike most mutants whose mutant powers emerge during adolescence, Madrox exhibits his gifts from the day he was born. As a result, recent issues of X-Factor have raised some question as to whether or not he is a mutant or something altogether different.