Nafs Asp

• WWizards of the Coast2004-10-04
  Official Ruling
  If it damages a player twice, they get to pay or take damage twice during their next draw step.
• WWizards of the Coast2004-10-04
  Official Ruling
  The ability does not cause itself to trigger again. It cause loss of life, and not damage.
• WWizards of the Coast2004-10-04
  Official Ruling
  If its damage gets redirected to its controller, it will still trigger the ability.
• WWizards of the Coast2004-10-04
  Official Ruling
  The player can pay the mana at any time after damage is done before the draw step of that player’s turn. People commonly pay during upkeep.

Rulings via Scryfall