Herald of War

The cost reduction is based on the total number of +1/+1 counters on Herald of War, not just the ones put on it by its own ability.

If there are additional costs to cast a creature spell, such as a kicker cost, apply those increases before applying cost reductions.

To determine the total cost of a spell, start with the mana cost or alternative cost (such as a flashback cost) you're paying, add any cost increases, then apply any cost reductions. The mana value of the spell is determined only by its mana cost, no matter what the total cost to cast the spell was.