Sorcery, 8R (9)
Rare
Blasphemous Act costs {1} less to cast for each creature on the battlefield.
Blasphemous Act deals 13 damage to each creature.
"Holy places are no longer sanctuary from death, and death is no longer sanctuary from anything."
—Thalia, Knight-Cathar
Illus. Daarken

9/22/2011: The total cost to cast Blasphemous Act is locked in before you pay that cost. For example, if there are three creatures on the battlefield, including one you can sacrifice to add {1} to your mana pool, the total cost of Blasphemous Act is {5}{R}. Then you can sacrifice the creature when you activate mana abilities just before paying the cost.
9/22/2011: Blasphemous Act's ability can't reduce the total cost to cast the spell below {R}.
9/22/2011: Although players may respond to Blasphemous Act once it's been cast, once it's announced, they can't respond before the cost is calculated and paid.
Legal in Vintage (Type 1)
Legal in Legacy (Type 1.5)
Legal in Extended (Type 1.X)
Legal in Standard (Type 2)
Legal in Classic (MTGO)
Legal in Commander
Legal in Modern