Forum:Nercovalley does it stop cost

i have a question whether or not using cards like exodia the ultimate forbidden lord or EUFL can use his cost of returning cards from my grave to the deck in order to summon him if nercovalleys on the field. i was told by one person here thats EUFL return monster is a cost thats returning cards and not a card effect, but another person tells me that its a card effect and that no cards can leave the grave while nercovalleys on the feild unless its the card themselves that allow themselvers to special summon them selves out of the grave.

so i would like to hear many replys so i can determine whether or not cards can actually leave the grave if nercovalleys on the feild.