Bone Mask

Damage prevention with a price tag, and the price is what makes the card worth talking about. Most prevention from this era (Healing Salve, the Circle of Protection cycle) asks only mana; this one bills you in cards from your own library, exiling exactly as many as the amount of damage stopped. That self-exile clause is the brake on what would otherwise be a repeatable, source-agnostic prevention engine: blank a small burn spell and you barely notice, but stop a large direct-damage finisher or a single hard-hitting attacker and you are pitching the top of your deck to save your life total. The number scales with the threat, so the card costs you most in precisely the situation where you most want it to work. The window matters just as much. The ability names a source and prevents the next instance of damage from it this turn, so you generally activate it reactively (responding to a burn spell already on the stack, or once blockers are declared), which means you usually know the size of the hit before you commit. What you cannot do is fog a full attack: it shields one source at a time, not the whole combat. And the library cost is not paid up front; it lands when the damage is actually prevented, scaled to whatever got through the door. It is built for a control posture that can afford to spend library as a resource, an early articulation of the idea that exiling your own cards is a real cost and not just flavor.