Elemental Resonance

The mana it makes is whatever you point it at, color and all, which makes this less a ramp spell than a multiplier you bolt onto your most expensive permanent. Enchant something that costs eight and you get eight mana of the right colors at the top of every turn, in addition to whatever that permanent already does. The catch is the same one that haunts every Aura: you are spending four mana and a card to upgrade a target that an opponent can answer, and the payoff only begins the turn after it resolves, on your main phase, after you have already untapped. So the design wants a board state that is already ahead, where doubling the mana off a fatty turns a strong position into an overwhelming one rather than digging you out of a bad one. The mana-cost-as-mana clause is the clever part of the build: it rewards casting the Aura onto the most extravagant thing you control rather than the safest, because the cost you are copying is the whole point. That tension (the more valuable the target, the more devastating its removal) is what keeps it a build-around curiosity rather than a staple. It is a ritual that refills, priced and timed so that you have to commit to a top-heavy plan before it pays you back.