Overclocked Electromancer

Overkill is normally wasted math: swing a 2/2 into a 1/1 and one of your two points of damage evaporates against a body that only needed a single hit to die. This card turns that surplus into currency. The power-doubling attack trigger is the engine that manufactures the overkill in the first place: the 2/2 body becomes a 4/2 on the swing, and any creature that blocks it may soak far more damage than its toughness can absorb, with every point of that excess refunded as stored energy. The smaller the blocker, the wider the gap between lethal and dealt: a lone 1/1 thrown in front of a doubled attacker converts one point of toughness into three energy. The optional counter payment sits on the other side of the exchange, spending three energy for a permanent size bump that then doubles into a bigger swing that then generates more excess than it cost to buy. Left uninterrupted the loop compounds, each combat step feeding the next. What holds the whole apparatus in check is the fragility of the 2/2 body and the requirement that the damage land on a creature: the refund only fires when a blocker eats the surplus, so an open board or an unblocked swing produces nothing at all. The payoff arrives in the narrow window where the opponent trades a body into your arithmetic, and vanishes the moment they refuse to.