Stacking is a term in Pillars of Eternity 2: Deadfire.
Stacking rules control how bonuses and penalties are added together. For simplicity, the game distinguishes four source categories of bonuses: passive, weapons, active/modal, and equipment.
All bonuses and penalties from passive sources and weapons stack.
Active and modal bonuses (e.g. from Abilities or consumable items) use the highest bonus and the lowest penalty to any given statistic. E.g. if a wizard spell grants +3 to Deflection and a paladin's aura grants +5, the active/modal bonus is +5, with the +3 being suppressed. If the same wizard spell also granted a bonus to Might, it would apply unless it was also trumped by a superior Might bonus from another active/modal source.
Equipment also uses the best bonus and worst penalty to any given statistic. It includes all items equipped directly on the character except for weapons. Equipment is a separate category from active/modal, so the best bonuses and worst penalties from each category are added together.
Afflictions (e.g. Stunned, Prone) are generally considered active effects. If an affliction is applied to a character while the same affliction is already active, it will replace the existing affliction's duration if the new duration is longer.
Stacking Notes & Tips