Source (Modal Double-Faced Cards (MDFCs) - Permanents/Spells - "The final category is interestingly what we had planned to do with the MDFCs in the first place—mix instants and sorceries with a permanent so you can squeeze more instants and sorceries into your deck. Each was designed to work synergistically in the same deck. There is a six-card cycle at rare, with each college getting one MDFC, as well as a colorless one. [...]")