This fella is Mabuz, he's technically death and knows. Though he's more evil with his powers and uses them to manipulate people. Eventually he's gone corrupt and now has tentacles and a eye that bleeds on a daily basis!

subzero is basically a manifestation of silver's rage and anger (n other things in his alter ego) that can either dwell in his mind, take over silver's body, or become a physical entity i'm thinking that subzero first came into being by silver getting cursed by sm in the sea, and that's why subzero's the kraken