Kazarov, purasangre de Sengir

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.

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.

Kazarov's triggered ability triggers once for each creature dealt damage at one time.