Battery Bearer

Turning a board of creatures into a mana battery is not new; what's specific here is the tax stapled to it. Every creature you control gains the ability to add a single colorless, but that mana is fenced off, unable to cast anything but artifacts. That restriction is the whole design conceit. In the abstract this is a Cryptolith Rite variant, except the mana it produces is deliberately crippled outside the artifact half of your deck, which is why the card can afford to hand the ability out for a four-mana body. The payoff clause resolves the tension: casting an artifact of mana value six or greater draws a card, so the fenced mana isn't just enabling big colorless bombs, it's paying you to cast them. That threshold matters. The reward is gated behind genuinely expensive artifacts, not the cheap gear an affinity shell floods the board with, which keeps the engine pointed at the top end of an artifact curve rather than a swarm of trinkets. The result is a build-around that wants two things at once: a wide enough creature base to generate real mana, and a heavy enough artifact top-end to convert that mana into cards. It rewards a specific deck shape rather than slotting into any artifact pile, and that specificity is what makes it a keystone rather than a filler enabler.