How does bolstering stack

Gameplay Dungeons, Raids and Scenarios
1

When a mob has 2 stacks, how is the final damage calculated?

a) BaseDamage * (1 + 0.2 * 2) = 1.4 * BaseDamage
Or
b) BaseDamage * 1.2^2 = 1.44 * BaseDamage

2

Quick research suggests that it’s additive by itself, so (a). That said, pulling trash into a boss can result in a bolstered boss, and Tyrannical is described on some of the search results I read as an effect that’s multiplicative with the key level. I don’t entirely have the brain-juice to crunch the numbers to tell you what COULD happen, but I can lay out the factors:
Enemy Health/Damage modifier applied just for the key (+15 as an example): 172%
Bolstering: 15% health and 20% damage on trash (and potentially a boss if you chain-pull), stacking additively with other stacks of Bolster (the way I understand it)
Tyrannical: 30% health and 15% damage for bosses, applied multiplicatively to the key level (I don’t know if this also applies multiplicatively to the Bolster stacks)

3

Why would it be exponential growth? It multiplies by stack count.

4

I’m unsure about the damage output but the health buff of bolstering is definitely multiplicative. This is how you got mobs up to millions of health in Legion and BFA; not really possible if it was additive.

5

I see. Thanks for the info.

So for keystone level it is multiplicative (exponential). Next level mob does 8% more dmg and have 8% more health.
Keystone 15 (m2 is base): 1.08^(15-2) ~= 2.7196 (about 172% increase)

Then bolstering is addictive on top of the keystone level base health/dmg.

For tyran boss health: keystone lvl base health * 1.3 * (1+ 1.2 * stacks)

“ I’m unsure about the damage output but the health buff of bolstering is definitely multiplicative. This is how you got mobs up to millions of health in Legion and BFA; not really possible if it was additive.”

Interesting, will try to watch some recorded videos and see how the mob health scales. I’d assume the damage scales similar way.

The confusion is that the affix description doesn’t specify if the increase is based on base health(addictive) or mobs current health (multiplicative)