The rare Odyssey artifact Charmed Pendant is one of a handful of cards that uses an example in its reminder text. The Pendant states that if you reveal a card that costs , you add to your mana pool.
So what card is referred to in the example? Editing wanted to use a real, unique card when they were devising the example, so they chose the only card with a mana cost listed as -- Spinal Embrace.
One other old card has a functionally identical mana cost: Legends' Princess Lucrezia's cost is written as . Back then, costs didn't follow the same rules they do now. Currently, all multi-colored mana costs are ordered clockwise around the color wheel. In the Oracle reference, Princess Lucrezia's mana cost appears in the current correct form -- identical to Spinal Embrace's .