99.9% credit goes to Nubtro, this is just an update of his list.
Most recent update: 3/26/23.
3/26/23: converted post into a Wiki.
4/28/22: Added Arreat’s Law to the Multiplicative category.
10/31/20: Moved Blade of the Tribes from additive to multiplicative.
3/17/20: Added H90 (Horde of the Ninety Savages) 6-piece and Undisputed Champion to multiplicative section.
12/9/19: Moved Depth Diggers, Enforcer, and Simplicity’s Strength from additive to multiplicative section.
12/6/19: I’ve updated everything I think has changed. If others could take a look and let me know if I’ve missed stuff, that would be appreciated. There are a few things here that I never knew about, like Call of the Ancients skill bonuses being multiplicative… anybody know if that is still the case?
> Damage Increased by Skills or “DIBS” category
> > these bonuses stack additively together
Active skills:
> Threatening Shout - Falter
> Battle Rage (including 15% for Marauder´s Rage)
> Rend - Mutilate
> Frenzy - Maniac
> Bash - Punish
> Cleave - Gathering Storm
Passives:
> Berserker Rage
> Brawler
> Sword/Dagger Weapons Master
Gems:
> Taeguk
> Gem of Efficacious Toxin
Gear:
> skill damage bonus rolls except Call of the Ancients
(a) Hammer, Whirlwind, Spear, Slam on helm and boots
(b) Frenzy, Bash, Cleave, Weapon throw on belt and pants
(c ) Rend, Furious Charge, Earthquake, Avalanche, Overpower, Revenge on chest and shoulders
(d)
> Dread Iron - Avalanche
> Strongarm Bracers
> Hexing Pants of Mr. Yan
> Harrington Waistguard
> Overwhelming Desire
> Oculus Ring <- before 2.4
> 300th Spear <- before 2.4
> Separate multipliers
Active skills and passives:
> Insanity
> Ruthless
> No Escape
Gems:
> Bane of the Trapped
> Zeis Stone of Vengeance
> Bane of the Stricken
> Bane of the Powerful
> Legacy of Dreams
> Simplicity´s Strength
> Enforcer
Gear:
Set:
> Wrath of the Wastes (2, 4, 6)
> Immortal King (6)
> Raekor (4, 6)
> MOTE (6)
> H90 (6)
> Legacy of Nightmares set bonus
> Focus + Restraint (each is separate 1.5x multiplier, 2.25x total)
> Istvan’s Paired Blades set bonus
> Endless Walk (i.e. Compass Rose + Traveler’s Pledge) set bonus
> Captain Crimson (3)
> Aughild’s Authority (2)
Legendary:
> Convention of Elements
> Vile Ward
> Standoff
> Lamentation
> Fury of the Vanished Peak
> Fjord Cutter
> Bracers of Destruction
> Gavel of Judgment
> Remorseless
> Bracers of the First Men
> Girdle of Giants
> Blade of Tribes -both Earthquake and Avalanche
> Skull Grasp
> Dishonored Legacy
> Oathkeeper
> Blade of the Warlord
> Undisputed Champion
> Mantle of Channeling
> Depth Diggers
> 300th Spear <- new 2.4 version only, old (white text) one was DIBS
> Arreat’s Law
> Skular´s Salvation (first bonus = 2.5-3x, second bonus = 2x, total 5-6x)
> Oculus Ring <- new 2.4 version only, old one was DIBS
> Squirt’s Necklace
Miscellaneous:
> elemental skill bonus (this group includes Enforcer gem)
> Call of the Ancients bonus (shoulders, chest, Boulder Breaker)
> damage bonus vs monster type (demons, humans, beasts, undead)
> elite damage bonus
Attributes:
> Strength