2016-09-20 : If a permanent has {X} in its mana cost, X is considered to be 0.

2016-09-20 : 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.

2016-09-20 : To determine how many cards to draw, use the mana value of the permanent immediately before you sacrificed it.