Madrox's power is the ability to create duplicates of himself at will through an unknown process whenever he is struck or even when he snaps his fingers or stamps his foot. Each of the duplicates 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 duplicate. The dupe usually appears to his side or often near a focused area, such as a finger.
During his time with X-Factor, the number of duplicates was probably around 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 duplicate that is "the part of you that can't be trusted" has announced that he plans to keep popping out.
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, he potentially can be attracted to every kind of person there is. 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. Along the way, he and/or duplicates participated in an Olympics gymnastics team and apparently became a licensed attorney.http://en.wikipedia.org/wiki/Multiple_Man