Food Chain

The mana this enchantment makes is locked to creature spells, and that one clause is the entire engine: it converts a creature on the battlefield into more mana than the creature cost, but only if that mana goes toward another creature, which can then be exiled for even more. The restriction sounds like a brake and is actually the accelerant; every spare point of mana wants to cast a creature with an enters-the-battlefield effect or a body big enough to end the game. The loop reveals itself the moment you find a creature that returns from exile rather than the graveyard, which matters because the ability exiles its creature as a cost. Misthollow Griffin is the classic partner: cast it with Food Chain's mana, exile it again for net creature-castable mana each cycle, and you have infinite of it. Squee, the Immortal does the same work, casting straight from the exile zone after Food Chain banishes it, so it never touches the graveyard at all. For years this sat as a curiosity, because the pieces it wanted (cheap creatures that recur from exile, and a sink to turn the infinite mana into a win) trickled out slowly across sets. What began as an obscure green enchantment with a fiddly restriction became one of the cleanest infinite-mana enablers in the game, its whole identity built on the two words "creature spells."