As an additional cost to cast this spell, sacrifice an artifact or creature.
Draw cards equal to the converted mana cost of the sacrificed permanent.
9/20/2016 If a permanent has in its mana cost, X is considered to be 0.
9/20/2016 To determine how many cards to draw, use the converted mana cost of the permanent immediately before you sacrificed it.
9/20/2016 If an effect copies Morbid Curiosity, the controller of the copy will draw the same number of cards as determined by the original. Its controller can’t and doesn’t have to sacrifice a permanent.