Blasphemous Act

• WWizards of the Coast2020-11-10
  Official Ruling
  Blasphemous Act's ability can't reduce the total cost to cast the spell below .
• WWizards of the Coast2020-11-10
  Official Ruling
  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.
• WWizards of the Coast2020-11-10
  Official Ruling
  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 , the total cost of Blasphemous Act is . Then you can sacrifice the creature when you activate mana abilities just before paying the cost.
• WWizards of the Coast2020-11-10
  Official Ruling
  To determine the total cost of a spell, start with the mana cost or alternative cost you're paying, add any cost increases, then apply any cost reductions (such as that of Blasphemous Act). The mana value of the spell is determined only by its mana cost, no matter what the total cost to cast the spell was.

Rulings via Scryfall