Origin

During the Inferno, N'Astirh sent Crotus & the other demons out to kidnap babies with power.   They went out into the human world & began stealing mutant babies, often killing the parents in order to do so.  N'Astirh used the babies to create a portal that led from Limbo to New York.  The combined forces of the New Mutants & the X-Terminators defeated N'Astirh & liberated the babies.  After New York had returned to normal, the New Mutants handed the orphaned babies over to the authorities.

Creation

Scab was created by Louise Jones Simonson and Jon Bogdanove and first appeared as a baby in X-Terminators Issue #2 (1988). Years later, he made his first appearance as an adult in New Mutants Issue #16 (2010). This version was created by Zeb Wells and Leonard Kirk.

Mayor Story Arcs

Project Purgatory

However, unbeknownst to the New Mutants, the government took the babies into their custody.  They were passed over to the care of the armed forces who treated the babies as potential weapons.   Project Purgatory was formed to take the infants to Limbo where time moved faster than on Earth.  In Limbo, the babies were brutally experimented on, often with triangular slices of skin being removed for testing. 
 
Project Purgatory was caught off guard by an attack of Limbo Demons led by Belasco's self-acclaimed daughter, Witchfire.  During the attack, the children managed to escape their bonds & fought the demons, successfully killing them all.  However, the confused message that was sent out indicated that the children had been killed.  Therefore, lost in Limbo with no means to return home, Project Purgatory continued to mould the mutant children into perfect living weapons.

New Mutants

During some down time after the events of the Second Coming, the New Mutants were unexpectedly taken into Limbo by Magik.  She could sense that Pixie had been kidnapped, and set out to save her.  However, Magik & the New Mutants were attacked.  The mutant children had spent the last 20 years living in Limbo, and they had learnt to attack individually & in a group.  

Sunspot

Scab fought the New Mutant Sunspot in a solo battle.  Despite Sunspot's own strength, Scab always seemed to have the upper hand.  Especially as the Brazilian New Mutant had been using a sword, which pierced Scab's skin & enabled his own mutant powers to flourish in battle.
 

Powers

Biological Based Armour

When Sunspot's sword pierced Scab's skin, it appeared that blood flooded out from the wound & instantly surged around the outside of his body.  Scab created a series of giant scabs that covered his body wherever he required it in order to protect himself, and to make his own punches even more brutal.