Electro, Assaulting Battery

A mana battery in creature form, breaking a rule as old as the game itself. Red mana normally empties from your pool at the end of every step and phase; the first line simply lets it stay, so a reservoir builds across combat, across your opponent's turn, across the whole cycle of phases rather than resetting the way floating mana always has. Feeding that reservoir is a triggered ability: every instant or sorcery you cast refunds a red, so a spell-heavy deck stops paying full freight on its second and third spells in a turn. Together the static and the trigger form a loop red has rarely been handed, because red has almost never been allowed to save mana across turns at all. The catch is where the payoff lives. That accumulated pool can fuel your spells and abilities in the meantime, but its dedicated payoff waits until Electro leaves the battlefield, at which point the leaves-play trigger cashes it out as direct damage to a player, scaled to whatever X you can afford. The 2/3 flier invites the trade, offering itself to removal and converting its own death into a burn spell. The design tension is that the more mana you bank while he holds the battlefield, the more you want him gone: a storage engine that only pays out when broken. Everything he does while alive is deferred value; the reward arrives at the exact moment the engine stops running.