Wily Goblin

Pay the double-red up front, get a Treasure back, and you have effectively bought yourself a mana you can spend later, in any color, and at any moment you could cast an instant: crack it end of turn, crack it mid-combat, crack it to hold up a splash-color trick. That deferral drives the whole design. The Treasure is stored fixing you cash on your own schedule, fuel for a cost-reduction shortcut, a splash the rest of the deck could not otherwise support, or an artifact for the engines that feed on them. The 1/1 body is incidental, a Goblin Pirate stapled to an enters trigger, though the type line at least earns its keep in a deck that cares about either tribe. Among the wave of creatures that turned the Treasure token from a flavor curiosity into a deckbuilding primitive, this is one of the plainer ones: no upside on the artifact, no scaling, no second token, just a single mana of any color attached to a creature you were already willing to run for the type line. What is worth noticing is not the creature or the token in isolation but the window between them: you pay now, and you decide later, at instant speed, what that mana becomes.