Nightfall is required to purchase and play Nightfall: Martial Law
Nightfall: Martial Law introduces many new characters, actions and new color combinations for creating chains and achieving kickers. Martial Law will also introduce the new “Feed” mechanic which will allow players to get even more uses out of their orders. The game also brings to the table a new “Wound” effect that is sure to surprise opponents!
Unlocking Promo Cards in Martial Law
Three Promo Cards are included in Martial Law as un-lockable extras! After you earn them, you can add them into your games!
Earning Achievements unlocks the promo cards and they will be visible in the Card Gallery. On the Create Game screen, touch the “Card Sets” button under your avatar to select which card set you'd like to play with, and to add or remove your unlocked promo cards!
Source: The Publisher Website.