Cold Mastery

Passive - increases the damage of your cold spells by piercing enemies' resistances to cold.

Cold Mastery is a Sorceress passive (Cold tree, level 30, no prerequisite) and the last skill in the tree. Unlike the fire and lightning masteries it adds no percentage to your damage: it lowers the cold resistance of whatever your cold skills hit, by 20% at level 1 and 5% more a level, 115% at level 20. Because a monster's resistance has a floor of −100%, the number that matters is where the mastery stops helping, which the Basin's page puts at level 17 against most monsters.

The numbers

The whole skill is one line. The row's passivestat1 is passive_cold_pierce and passivecalc1 is ln12, which is Param1 (20, the table's "Cold Resistance reduction baseline") plus Param2 (5, "Cold Resistance reduction per level") for every level after the first: 40% at level 5, 65% at level 10, 100% at level 17, 115% at level 20, 165% at level 30. The expression reads lvl, so +skills from gear raise it like hard points. There is no mana line.

How it works

The passive state "coldmastery" carries the stat passive_cold_pierce while you have the skill. The Basin's page says it reduces the target's cold resistance when the Sorceress applies cold damage, cold length or freeze length to it, so it works like Enemy Cold Resistance Reduction on an item, see Resistances and Immunities for where that sits. It does not apply to cold damage dealt by allied players, mercenaries or pets, only to the Sorceress's own. It does not apply to a monster that is immune to cold: an immunity is not pierced.

The Basin's page gives the rule that makes it a damage skill: the reduction lowers both the cold damage and the cold or freeze length by the same resistance, and a target's resistance can be driven down to the −100% floor, where the cold damage and the chill or freeze are both doubled. From there the mastery can do no more. The Basin's arithmetic: a level above 17 (−100%) is potentially redundant against monsters, and a level above 37 (−200%) is always redundant against a non-sundered monster.

Against a monster whose cold immunity has been sundered by a charm (Monster Cold Immunity is Sundered) the Basin says the mastery applies at one fifth of its value in D2R: a level 20 mastery is −23% there, and level 30 is −33%, so the higher levels keep paying against sundered targets long after they stop paying against ordinary ones.

The mastery cannot break an immunity: a monster at 100% or more cold resistance takes nothing from a cold skill whatever the level, unless a sunder charm first brings it below 100%, and then the mastery counts at a fifth.

Synergies and +skills

Cold Mastery has no synergies and feeds no synergy line. Its one line reads lvl, so every +skill is worth exactly a hard point: −5% enemy cold resistance. Because the −100% floor is reached at level 17, +skills and hard points past that level are worth nothing against a monster that is not sundered, and everything against one that is.

Against players

Cold Mastery is a passive on yourself and never touches a player directly; the cold hits it strengthens are cut to 17% of their value against a player by the player-versus-player rule, see Player versus Player. The Basin's page notes that higher levels still matter against players and mercenaries who stack cold resistance above the cap: its example is a player applying 350% cold resistance in Hell, where the difficulty's penalty is −100%, who is still at 50% after a level 37 mastery, halving the cold damage and cold length.

Build notes

• Level 17 (−100%) is the target against ordinary monsters; a Sorceress with +8 skills from gear needs 9 hard points to reach it, and the rest of the points are better spent on a synergy that reads hard points.
• The −100% floor is a doubling: from 0% to −100% a cold skill lands at twice its number, and from 75% to −25% at five times.
• Against sundered immunes every level counts at a fifth, so a level 30 mastery is −33% there and the "wasted" levels are the ones doing the work.