Marrow

Sarah Rushman better known as Marrow is a mutant in the X-Men series. She is a mutant with a different mutant power: detachable bones grow right through her skin. She is a member of the sewer dwelling mutants the Morlocks. Marrow was embittered by the harsh life she lived, first in the Morlocks' dark tunnels, and then fighting for survival in the dimension she was sent to by an evil mutant named Rasputin. Despite her hostile attitude, Wolverine decided to become her mentor when she joined the X-Men. He succeeded in training her to work as a member of the team. As Marrow slowly mellowed, she grew close first to Gambit, and later to Colossus.

History
A mutant able to control her bone growth, providing her with armor, clubs, and knives. As a child, she was taken in by the Morlocks where she would form the terrorist group Gene Nation before joining the X-Men. Her allegiances have shifted frequently since then. She was de-powered after M-Day.

Sarah's real name is unknown, as well as her place of birth or who her parents really were. From a young age she manifested bones which grew out of her face. This obvious mutation led her to be taken in by the Morlocks - mutants that felt themselves too hideous to live above ground - cursing herself to a life underground. She may even have been among the first group of Morlocks.

As an adult she often fought the X-Men, partly because she felt that their fight for peaceful co-existence with humans was foolish and also for revenge because of their inability to save the Morlocks during the Mutant Massacre. Some say she was jealous of their beauty and ability to be normal as well.

Sarah was a little mutant with the mutant power to see kindness in every person. She was a very close friend to Callisto, who saw her as a daughter. Marrow is one of the few surviving Morlocks to join Callisto'sNew Morlocks which is a group of mutants and humans living together.