Whenever one or more cards are put into exile from your graveyard, put that many +1/+1 counters on Rakshasa Vizier.
Exiling cards from your graveyard to pay the cost of a spell with delve is a single action. It will cause Rakshasa Vizier’s ability to trigger once, putting a number of +1/+1 counters on it equal to the number of cards you exiled.
If a card is exiled “instead” of being put into a graveyard, Rakshasa Vizier’s ability won’t trigger.