Ventifact Bottle

A mana battery that charges on your terms and discharges on its own schedule, and the catch lives entirely in that timing split. You pour mana into it at sorcery speed, paying to bank counters, but you do not get to choose when the bottle pays out: it empties automatically at the start of your first main phase, tapping itself and giving you colorless mana equal to whatever you stored. The release is mandatory and self-tapping, so the bottle is unavailable for anything else the turn it discharges, and you cannot hold the charge to skip a turn or bridge across a sorcery-speed mana sink the way Mind Stone or a basic ritual would let you. It is a converter that trades flexibility for raw delayed acceleration: invest one turn, collect a fat colorless payment the next. That rigidity is what kept it on the margins; the cost of charging plus the loss of the activation turn makes the math rarely beat just casting your spells directly. As one of Mirage's stranger artifacts, it reads more like a design experiment in deferred mana than a card built to win games, an early sketch of the "store now, spend later" battery space that later sets would refine into cleaner, more controllable tools.