GOG forums get no love. But anyway, effective damage. You may have noticed when in combat that sometimes your damage numbers have yellow chevrons next to them, pointing up. Any time you see this, you are doing what the Arena considers effective damage. Most commonly, this is damage that exploits an elemental weakness, or damage done while an enemy is broken. The effective damage awarded is the amount in excess of whatever the base damage would have been (e.g. if you attacked in neutral, or the enemy wasn't broken).