Nessian Demolok

Tribute is a static ability that functions as the creature with tribute is entering the battlefield. “Tribute N” means “As this creature enters, choose an opponent. That player may put an additional N +1/+1 counters on it as it enters.”

Objects with tribute have triggered abilities that check “if tribute wasn’t paid.” This condition is true if the opponent chosen as a result of the tribute ability didn’t have the creature enter the battlefield with +1/+1 counters as specified by the creature’s tribute ability.