The attack value of a Hero is used as the base value for each hit done by weapons aligned to the color of the Hero. The actual damage caused, depends largely on the defense value of the opponent and the attack value of the weapon but there are many other variables at play as well.

For example, hitting two enemies at once divides the damage evenly for both of them. Having multiple heroes of the same color increases damage done by that color and naturally, the color modifiers also affect the damage by a large degree.