Metamorphosis

Channel as a creature spell, with the wrinkle that the floor is set by what you eat. The math is the design: sacrifice a creature with mana value N, get N+1 mana of one color, all earmarked for the next creature on the stack. That floor of "one plus" is what keeps the card honest at one green; a freshly summoned dork is worth two mana toward something larger, and a small-creature-into-fatty curve compresses turns in a way green's usual land-based ramp does not. The color-fixing clause is the quietly radical part. This is mono-green producing off-color mana without an artifact, without an enchantment, without a land, without a tapped permanent: a sorcery that launders green creatures into blue or black or red or white, restricted only by what you spend it on. The restriction is doing real work, because without the creature-only clause this would be a one-mana off-color ritual scaled by sacrifice, a different and much louder card. As written, it is a transmutation engine: the small creature you no longer need becomes the large creature you want, in whatever color that creature happens to be. The mechanic has barely been revisited; most of green's later sacrifice-for-mana lines kept the mana the same color it came in as, which makes this early experiment in cross-color conversion stranger and more singular than its one-mana cost suggests.