The answer is One or both faces of a double-faced card may include a reminder about what's on the other face
These are Elbow Strike and Slicing Blade
For added redundancy, the deck includes Greed's Gambit as an alternative to Demonic Pact
Of those eighteen, I could include three white, three blue, three black, three red, and three green cards (fifteen total), leaving me with three empty slots
Abyssal Persecutor Angel's Grace Approach of the Second Sun As Luck Would Have It Azor's Elocutors Barren Glory Battle of Wits Biovisionary Call the Spirit Dragons Celestine Reef Central Elevator // Promising Stairs Central Elevator // Promising Stairs Chance Encounter Cloudsteel Kirin Coalition Victory Courageous Resolve Darksteel Reactor Doctor Doom, Unrivaled Duelists' Convocation International (playtest) Epic Struggle Everybody Lives
For example, the Beginning Phase contains the Untap Step where you untap all the cards you tapped last turn, the Upkeep Step where various ongoing card abilities take effect, and the Draw Step where you draw a card