I think you might be referring to a different "form of payment". See, there's resources and Shadow Energy. Resources are created by sacrificing cards, which I'm sure you know of. Shadow Energy, on the other hand, are accumulated by your hero per turn (sub the first turn if you went first). It's the number on the lower left-hand side of your hero. Some hero abilities, including weapons and armors, require Shadow Energy and not Resources for their effect to be activated. This is what I think you might have missed.
Bookmarks