Courtesy of Wizards of the Coast (WotC) and Rocket Beans, check out two iconic “free spells” from Doubles Masters — Chrome Mox and Manamorphose!
Originally printed in Mirrodin (with reprints in Eternal Masters, Masterpiece Series: Kaladesh Inventions, and as a Grand Prix promo foil), Chrome Mox has been banned in Modern for quite some time, but has seen play in Legacy and Vintage along with Commander. Few imprint cards have been as relevant as Chrome Mox after the mechanic debuted in Mirrodin and now it is back as a mythic rare with new art as a box topper.
Originally printed in Shadowmoor (with reprints in Modern Masters: 2013 and Mystery Booster) Manamorphose doesn’t cost zero, but it is effectively free and is rarely played in a fair fashion. The Modern Storm enabler allows the deck to churn through its deck while doing even more with other combo pieces on the battlefield.