Niv-Mizzet, the Firemind

• WWizards of the Coast2018-03-16
  Official Ruling
  If dealing 1 damage to a permanent or player causes you to draw a card, perhaps because Niv-Mizzet is enchanted by Curiosity, you'll continue this loop until the loop is interrupted, perhaps by a player losing the game.
• WWizards of the Coast2018-03-16
  Official Ruling
  If a spell or ability causes you to draw multiple cards, Niv-Mizzet's ability triggers that many times.

Rulings via Scryfall