he looks metallic so i would say that he was attacked by a secret military experiment. A biomechanical monster (meaning biological machine) which was a carrier of a disease that caused the calcium in your bones to solidify into metal. The first symptoms you will have stronger bones, then stronger muscles as the infection spreads, followed by your skin tissue being torn away by the metal, replacing your skin but keeping your viens and vital organs intact. As symptoms get worse, the cells in your body start reproducing frantically, causing spikes to appear all over your body and get larger as time goes by, veins will start to grow in the place of these new spikes and become a part of your body. The virus itelf would have to be a mechanical disease similar to what causes Elephantiais. Elephantiasis is already known to cause grotesque mutations causing parts of the body to become as hard as bone, the virus that changed this character would've work the same as this, turning bone into steel instead and spreaded throughout his body. Eventually the infected will die when the metallic tissue replaces all of his body and turns him into a large, spiky steel statue.
As symptoms get worse, the cells in your body start reproducing frantically, causing spikes to appear all over your body and get larger as time goes by, veins will start to grow in the place of these new spikes and become a part of your body. The virus itelf would have to be a mechanical disease similar to what causes Elephantiais.
Elephantiasis is already known to cause grotesque mutations causing parts of the body to become as hard as bone, the virus that changed this character would've work the same as this, turning bone into steel instead and spreaded throughout his body.
Eventually the infected will die when the metallic tissue replaces all of his body and turns him into a large, spiky steel statue.