Celestial Mantle

If the enchanted creature’s controller has a life total below 0 (which is possible if that player controls Platinum Angel, for example), Celestial Mantle’s triggered ability multiplies that number by two. For example, if the player had -4 life, that player’s life total becomes -8.

At the time the ability triggers, determine which creature Celestial Mantle is enchanting. As the ability resolves, determine who currently controls that creature (or, if it’s no longer on the battlefield, determine who controlled it when it left). That’s the player whose life total is doubled. It doesn’t matter who controls Celestial Mantle, who controlled the creature at the time the ability triggered, or what creature Celestial Mantle enchants at the time the ability resolves.

If a creature dealing combat damage at the same time as the enchanted creature has lifelink, the life gained due to lifelink happens before Celestial Mantle’s triggered ability resolves.