What are the most cost-efficient cards in the game?
I realize this is somewhat subjective, as cost does not take into account faction - some factions have the ability to accelerate power by adding resources or refreshing domains, so their cards arguably "cost" a bit less; likewise with supports that can often be played as a card effect. But I still think it's an interesting question.
My vote: Y'Golonac. It has Invulnerability, two Terror (and so is immune to insanity) and a Combat and an Arcane, skill 4, and can either pull either a friendly character onto its story to help out, or an enemy character to its doom. It's amazingly versatile, one of the best Ancient Ones in the game. Its only weakness is that it is unique, but that's hardly a weakness given its strengths. Is there ever any reason not to run Y'Golonac in a Shub deck? And what was the design team thinking giving it a cost of only 4?
I can think of a few other cards that may be contenders for the most cost-efficient, but I'm interested in other thoughts.