Arterial Flow

• WWizards of the Coast2018-01-19
  Official Ruling
  In a Two-Headed Giant game, Arterial Flow causes the opposing team to lose 4 life, and each player on that team discards two cards. You gain 2 life.
• WWizards of the Coast2018-01-19
  Official Ruling
  Arterial Flow causes each opponent to lose 2 life if you control a Vampire, even if some or all of those players were unable to discard any cards.
• WWizards of the Coast2018-01-19
  Official Ruling
  Whether you control a Vampire is checked as Arterial Flow resolves.

Rulings via Scryfall