Kazarov, Sengir Pureblood

• WWizards of the Coast2018-04-27
  Official Ruling
  If Kazarov is dealt damage at the same time that a creature an opponent controls is dealt damage, Kazarov must survive the damage to get a +1/+1 counter.
• WWizards of the Coast2018-04-27
  Official Ruling
  If a creature is dealt an amount of damage "for each" of something, that damage is dealt as one event and Kazarov's triggered ability triggers only once.
• WWizards of the Coast2018-04-27
  Official Ruling
  Kazarov's triggered ability triggers once for each creature dealt damage at one time.

Rulings via Scryfall