Doppelgang

The math is the entire point, and it is quadratic. Most copy effects are additive: pay a cost, get one duplicate of one thing. This one squares its input twice over, because X does double duty as both the number of targets and the number of copies made of each. Spend enough to hit X of 4 and you are not making four tokens, you are making sixteen (four copies each of four permanents); at X of 5 it climbs to twenty-five. The in the cost is the counterweight, tripling the tax on every point of X so the curve stays payable only when the ramp is genuinely there. That structure is what makes it a payoff rather than a value spell: it does nothing efficient at small numbers and everything at large ones, so it lives in decks built specifically to overload the middle of the game with mana. The target line is deliberately permissive, too. It copies any permanents, not just your creatures, which means the copies can be lands and mana rocks as easily as bodies, letting a resolved cast fund the next explosive turn as readily as it wins on the spot. Build-your-own-fireball copy spells scale a single duplication linearly with mana; this one instead rewards a mana total high enough that the second factor of X stops looking like a rounding error and starts looking like a board.