Erik Lauer previewed four cards for Modern Masters in his article Developing Masters today: Masked Admirers (rare from Lorwyn, uncommon in #MTGMM), Life from the Loam (rare from Ravnica, rare in MTGMM), Stinkweed Imp (common from Ravnica, common in MTGMM), and Worm Harvest (rare from Eventide, uncommon in MTGMM). The Stinkweed Imps in Modern Masters will use the alternate art found on Duel Decks: Divine vs. Demonic Imps.
Mark Rosewater's article Token of Appreciation had four more preview cards: Thallid (Fallen Empires/Time Spiral common, MTGMM common), Thallid Germinator (Time Spiral Common, MTGMM common), Cloudgoat Ranger (Lorwyn uncommon, MTGMM uncommon), and Doubling Season (Ravnica rare, MTGMM rare). The new Doubling Season will use the alternate art found on Judge Promo foil Doubling Seasons.
View our Faceboook album of all Modern Masters cards spoiled here.