Farsight Mask

• WWizards of the Coast2004-12-01
  Official Ruling
  You draw no more than one card each time a source an opponent controls damages you, no matter how much damage the source deals.
• WWizards of the Coast2004-12-01
  Official Ruling
  Each instance of each creature’s combat damage is counted separately. If three creatures with double strike attack you and all of them are unblocked, you may draw up to six cards.
• WWizards of the Coast2004-12-01
  Official Ruling
  This triggers each time a source an opponent controls deals damage to you. If the same source deals damage more than once in a turn, it triggers for each of those times.
• WWizards of the Coast2004-12-01
  Official Ruling
  Farsight Mask must be untapped both when the damage is dealt and when you would draw the card.

Rulings via Scryfall