Deadly Strike is a chance to deal double damage on a weapon attack in Diablo II. It is provided by some Rune Word, Unique, and Crafted item properties, mostly weapons, as well as the Lo Rune. The damage is doubled after all other bonuses, including Strength and Dexterity modifiers.
Chance to Deadly Strike stacks additively when multiple items provide it. Deadly Strike does not stack directly with the Assassin's, Barbarian's or Amazon's Critical Strike chance, which also does double damage, but if both are present, the game will roll for one effect, and then the other if the first fails. However, a single attack cannot get both bonuses, so the maximum multiplier is double damage, not quadruple damage. The chance to achieve this is multiplicative - only the percentage of attacks that are not Critical Strikes have a chance to Deadly Strike. Therefore the chance to double damage is:
CS + DS*(100-CS)/100
So:
- A character with 25% Critical Strike and 25% Deadly Strike has:
25 + 25*(100-25)/100 = 43.75%
chance to double damage. - An Amazon with 68% Critical Strike and 50% Deadly Strike has:
68 + 50*(100-68)/100 = 84%
chance to double damage.