Morbid Curiosity

Sorcery

As an additional cost to cast this spell, sacrifice an artifact or creature.
Draw cards equal to the mana value of the sacrificed permanent.

2016-09-20:
If a permanent has {X} in its mana cost, X is considered to be 0.
2016-09-20:
To determine how many cards to draw, use the mana value of the permanent immediately before you sacrificed it.
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.