Kethis, the Hidden Hand

The card that finally made "legendary matters" more than a supertype-counting curiosity, and it did it by turning the graveyard into a renewable resource. The discount is the loud half: every legendary spell you cast comes down cheaper, letting a deck of unique permanents outrun its own mana curve. The recursion is where the design earns its reputation. The activated ability exiles two legendary cards from the graveyard to grant every other legendary card there a from-graveyard clause for the turn, and that inversion of cost is the whole engine. Because the ability counts cards rather than mana value, a critical mass of cheap legendary permanents beats a handful of expensive ones: many small legends feed the exile cost while unlocking the rest, and every legend that dies again simply refills the bin. The two halves loop into each other, since those graveyard legends get replayed as legendary spells, so the discount applies to each one on the way down. Cast legends, let them die, exile a pair to replay the survivors, repeat. That structure is exactly why the card lived a double life away from any singleton restriction: given a mana outlet and enough cheap legends, the exile-and-replay clause becomes a genuine engine, one that churns a graveyard into repeated casts. The design points an entire archetype at a card type most decks treat as incidental flavor text.