707.2. Face-down spells and face-down permanents have no characteristics other than those listed by the ability or rules that allowed the spell or permanent to be face down. Any listed characteristics are the copiable values of that object’s characteristics. (See rule 613, “Interaction of Continuous Effects,” and rule 706, “Copying Objects.”)

Double-Faced Cards Rules Changes

1. Converted mana cost

Remember when I said that the characteristics of the face that's up are all that matter? That wasn't quite accurate. Under the new rules, the converted mana cost of the back face of a DFC is based on the mana cost of the front face. (Previously, because the back faces lacked mana costs, their converted mana costs were all 0.) The one exception is if something is a copy of the back face of a DFC, its converted mana cost is 0. So If I control Insidious Mist [transformed version of Elusive Tormentor], it has no mana cost, but its converted mana cost is 4. If I then put a copy of Insidious Mist onto the battlefield, that copy's converted mana cost is 0.