Accumulation Formula and Diminishing Rule of (De)buff [Un-stackable]

Skills and VCs of the same name do not accumulate their effects unless otherwise they are specifically mentioned "stack"
Skills and VCs of different names and the same category do accumulate their effects

Accumulation Formula

The total multiplier of (de) buffs accumulated is determined by the sum of the following (i), (ii), (iii)...(n) as the following diminishing rule is applied to:

(i) most effective (de)buff (%)
(ii) second most effective (de)buff (%) * (i)
(iii) 3rd most effective (de)buff (%) * (ii)
...
(n) nth most effective (de)buff (%) * (n-1)

When you use the following skills of the physical resistance buff, the total resistance multiplier is 37.65 %:

Character	Skill	Multiplier	Diminished
Nomar	Phalanx Guard	+30%	+30%
Myrus	Terra Fortress	+25%	+7.5% (30%*25%)
Anabel	Gardian Soul	+20%	+0.15% (7.5%*20%)

Diminishing Rule Among (De)buff Categories

The diminishing rule is applied to (de)buffs on a category Lv. 2 basis. If in the above example, +20% slash resistance is used, the total multiplier against a slash attack is 37.68% (+0.15%*20%). When, on the other hand, you use +50% all-elemental resistance buff instead of the slash resistance, the total against an elemental slash attack is 87.65% (37.65+50) because the diminishing rule does not apply to the different category and the multipliers are simply added.

Example

Suppose the buff skills from A. to D. are used.

Category	Physical Resistance	Elemental Resistance
	A. Physical+30%	C. All-elemental+50%
	B. Slash+20%	D. Fire+50%

The total multipliers of buffs against the following types of attacks are as follows:

Attack types	Total Multiplier	Note
Fire Blunt	105%	A.+C.+D.
Fire Magic	75%	C.+D.
Wind Slash	86%	A.+B.+C.
Wind Magic	50%	C.

Simplify