Progenitor Exarch

The design idea sits in the doubled X. Because both symbols draw from one value, each point you pay for costs two mana and buys one incubate 3, so setting X to three costs seven mana and seeds three dormant 3/3s in Incubator form. The scaling is linear, but the payload is deferred: an Incubator does nothing until you spend the transform cost, so the enters-the-battlefield burst is a stockpile of promissory notes rather than an immediate board. That separation between creation and activation is the balancing mechanism. You have already paid to make the army; you still have to buy it back one Incubator at a time. The tap ability softens the toll by converting a single token per turn for free, but one flip per turn is a slow drip against a large reserve, and it ties up the 1/2 body to do it. Read the whole thing as a token generator that manufactures potential energy and then rations its release: two clocks for cashing in, raw mana or the creature's own tap, whichever you can afford. The Phyrexian framing dresses it up, but structurally it is a swarm engine that hands you the swarm in advance and makes you collect it a creature at a time.