Below you can find a short summary about damage multipliers in BIS. Alternatively you can check my video on the same topic: link
Why is this important?
Because it affects how skills interact with each other and allows you to understand which stat is better to stack (with War Souls, hones and buffs) on which unit.
The BIS damage formula has the following form:
Base Damage ✖ Multipliers
Every Multiplier has the following form:
1 - defender defensive bonuses + attacker offensive bonuses
For example Damage Rate (DR) and Damage Reduction Rate (DRR) affect the same multiplier which I call the Rate Multiplier. In a simple though experiment where defender has 10 % DRR and attacker has 25 % DR the Rate Multiplier is:
1 - 0.1 + 0.25 = 1.15
And if the game would only have the Rate Multiplier a simple 1m base damage attack would then deal:
1m * 1.15 = 1.15m
However, various tests have shown the game does have other multipliers. I have currently discovered 4 but there could be more or more could be introduced later. I named the multipliers either with something that seemed logical or some memorable skill that lead to their discovery. The multipliers are:
You can find more details on the sources of modifiers for these multipliers on their respective pages. The existence of these modifiers turns the damage formula into:
Base Damage ✖ Rate Multiplier ✖ Cat M. ✖ Spec M. ✖ Eye M.
If we continue our hypothetical example from above, but now assume that 1m base damage would be from Vasto hitting Sode with rage and that Sode has full HP and is fielded in a maxed Sage Hall formation then the damage calculations would look like:
1m * (1 - 0.1 + 0.25) * ( 1 - 0.4) * (1 + 0.1) * (1 + 0.6) = 1m * 1.2144 = 1.2144m