Rapid Cell Regeneration
All the cells in Shaw's body are in a heightened state of regeneration. They split and divide at a much faster rate then normal people's cells, causing wounds and infections to be repaired very quickly.
Healing
Shaw can heal back from any wound as long as it does not stop the function of a certain part of his brain. He can not heal his body with larger objects still in it, but smaller objects such as bullets can be expelled by the body with ease as a part of the healing process. In this same thread of thinking, his body parts must be in their proper place before healing may occur — such as setting his bone so it can heal. If the wound is a large one, such as being laid open on a coroner's table, he needs to hold the wound closed until it can knit together. Blood is never drawn back into his body, which means that he's left a bloody mess no matter what happens.
Another aspect of his healing is her ability to heal others. If a measured amount of his blood is injected into someone, it will heal them from any injury, regrow missing limbs and tissue, and even bring them back if they are freshly dead. Again, the same limitations apply. (e.g., broken body parts having to be in place and objects removed, etc.)
Regrowing Parts
Even after he loses a limb, Shaw's ability can direct his cells into remembering what was there and reform it. The wound must be fresh, so he might have to open up an older wound to give his body something to work with. It is likely that the process would be uncomfortable and even a bit painful.
When it comes to someone else's limb he cannot regrow what was not there in the first place. He cannot use his blood to grow anything not written into someone's DNA (e.g., genetic mutations, birth abnormalities, etc.)
High Pain Tolerance
Due to the fact that his body repairs so rapidly, this has the side effect of increasing Shaw's pain tolerance. He feels pain just as intensely as the next person, but the pain goes away quickly. While he hurts like hell, he can still function through the pain and do whatever needs to be done.
Immortal
Due to the fact his cells are always in a heightened state of activity, Shaw will never die of natural causes, nor will he age or get sick in any way. When his body reaches the age that cells start to die off, his will not. Due to his rapid cell regeneration, he's also able to survive a number of otherwise fatal injuries. He can still be killed by other methods that work against his ability, such as decapitation or severe brain damage.
The Off Switch
There is a microscopic spot in Shaw's brain at the back of his skull that, if hit, turns off his ability and allows him to die. However, this only lasts as long as there is something wedged into that site. Small items, including bullets, will be expelled. Once the object has been removed and the degeneration to his body isn't too far along, he should be able to come back to life. He can be killed if his ability is otherwise suppressed or negated, his head or brain is removed, or by drowning as he cannot live without access to oxygen. If the conditions are rectified in time and his regeneration is able to restart, he can come back to life.
