Breathstealer

Each black mana spent here trades a point of survivability for a point of damage, so the 2/2 body becomes a 3/1, then a 4/0 that dies the moment its own ability resolves. The Nightstalker tribe of Mirage was built around exactly this self-destructive math, with several members sharing variations on the +1/-1 valve. What the design buys is a creature that can punch through a low-toughness blocker or push exact lethal late, at the cost of folding to any removal that cares about toughness and to over-activation. Because the modifier lasts only through the current turn, the calculation resets with every combat: you spend precisely what the moment demands and no more, so the activation stays a scalpel rather than a self-inflicted wound. It is a small, honest creature from an era when black bodies were expected to pay for their effects with their own flesh, and the toughness-for-power bargain is the cleanest expression of that idea in the cycle.