There are a number of cards in Ravaged Worlds that you will not find in any booster. These cards can only be gained by achieving a number of conditions and every week a new set of Achievement cards will be made available to win.

Achievement cards are awarded once per night

Battering Ram
A weapon straight out of batman's repertoire. This nifty little gadget will constantly deal dmg to your opponent's cap, and the more creatures you have deployed, the bigger the punch. I really wish this attachment was a neutral one, because it would definitely be included into all of my decks
Most versatile card in the game. Costs 0 to play makes you draw and can either remove and attacker or a blocker from combat on top of having that creature return locked on the next turn. What Keb deck should not run 4 of these!