If you fail and flip over a skull, you lose one of your four cards (either chosen randomly by an opponent or one you choose yourself, depending on where you found the skull)
Overlapping Synergies Going off of my last point its also vital to know how certain mechanics synergize with each other over both sets
Carmen does cost five, though, so the rest of your deck should be filled with equal amounts of recursion (Sevinnes Reclamation et al), ramp (Ancient Tomb, Sword of the Animist) and evasive bodies that can also grow tall (Voldaren Bloodcaster, Liberator, Urzas Battlethopter, Serra Ascendant)
Prices of Warhammer 40,000 cards began to decrease slightly following the previews
Plus, you get to align yourself with one other player which is sometimes better than granting the whole table an extra card