Verdant Eidolon

A green mana and a sacrificed 2/2 convert into three mana of a single chosen color: a ritual stapled to a body, with one crucial back end. The recursion clause keys off the exact spells a color-greedy pile most wants to cast, so every gold card you cast buys the option to return this Spirit from the graveyard to your hand and run the filter again. Treat the loop honestly, though, and it is a fixing engine rather than a ramp engine. Each cycle costs to recast plus to activate, and gives three mana back: a net loss of two mana per loop, paid in colorless flexibility to receive three of any single color you are short on. The loop never makes mana; it launders it, taking whatever your lands produce and converting it into the precise color a multicolored hand needs. That builds in a chicken-and-egg cost: you have to already be casting gold spells to fire the recursion, so the first cast is a real investment, and every loop afterward amortizes that investment rather than erasing it. The 2/2 frame is incidental. What you are buying is a renewable color filter that keeps coming back as long as the spells stay colorful, smoothing the manabase at a small, deliberate price each time you draw on it.