{Diluvian Primordial} comes into play. I search my opponents graveyard and find an entreat the Angels. How would the x in its mana cost be treated? Or would I not be able to cast it?
Whenever you cast a card without paying its mana cost, any value of X is treated as 0. You may cast it, but it wouldn't do much!
RESOLVED
Ah .poo. lol I passed on it in the grave because I was not sure of the legality of the move. But your explanation made the most sense. Thanks!