Spell Resistance is most beneficial for encounters that involve heavy, tank-directed spell damage. It becomes increasingly more effective for the encounter if most or all incoming damage is elemental, such as Hydross and Illidan.
Party or raid-wide elemental damage does not always necessitate or benefit from heavy Spell Resistance gear on the tanks. For example, Hex Lord Malacrass and Sapphiron both use raid-wide spell damage but still primarily use Physical damage on the tank. In these situations, it is more effective to wear full tanking gear (with an emphasis on Health) and only add Resistance gear when you clearly surpass gearing requirements.
Some encounters -- Hydross and Illidan in particular -- benefit from 490 Defense or a combination of Defense and Resilience to reach the Crit Reduction minimums. To achieve this, one of the most cost effective pieces of gear is an Arena shield providing both Resilience and high Health. If you fall just short of the recommendations, it is ok to be slightly short on Crit Reduction for Illidan or Resistance for Hydross; this is survivable burst damage on Hydross and Illidan, but
be sure to reach the minimums as soon as possible. Be aware that Mother Shahraz off-tanks wearing Shadow Resist gear do not need to worry about Crit Reduction, as NPCs cannot Crit with special abilities.
Please note that Avoidance is still effective against elementals such as Hydross and Illidan flames. However, Shield Block is not, and the Shield Block ability should not be used. In some situations where gearing minimums are met it is possible to effectively dual wield for additional Threat.
The maximum effective resistance for a level 73 target is 365 Resistance. 365 Resistance will, on average, reduce 75% of incoming damage. With raid buffs from other classes (particularly Paladins and Shamans), 295 Resistance on gear will allow you to reach the 365 cap.
Resistance Gear (Frost, Hydross) [Iceguard Leggings] - Blacksmithing - Violet Eye Exalted Reputation
[Iceguard Breastplate] - Blacksmithing - Violet Eye Exalted Reputation
[Iceguard Helm] - Blacksmithing - Violet Eye Exalted Reputation
[The Frozen Eye] - Jewelcrafting - Violet Eye Honored Reputation
[Pendant of Thawing] - Jewelcrafting - Lower City Revered Reputation
[Inscription of Endurance] - Violet Eye Honored Reputation
[Glyph of Frost Warding] - Keepers of Time Honored Reputation
[Frost Armor Kit]x4 - Leatherworking
Crafting Totals
48 Khorium Ore, 4 Eternium Ore, 6 Fel Iron Ore, 4 Khorium Ore, 3 Primal Nether, 6 Primal Water, 64 Primal Fire, 5 Primal Earth, 20 Adamantite Powder, 16 Heavy Knothide Leather
Resistance Gear (Nature, Hydross) [Wildguard Leggings] - Blacksmithing - Cenarion Expedition Exalted Reputation
[Wildguard Breastplate] - Blacksmithing - Cenarion Expedition Exalted Reputation
[Wildguard Helm] - Blacksmithing - Cenarion Expedition Exalted Reputation
[The Natural Ward] - Jewelcrafting - Cenarion Expedition Exalted Reputation
[Pendant of Withering] - Jewelcrafting - Scryer Revered Reputation
[Inscription of Endurance] - Violet Eye Honored Reputation
[Glyph of Nature Warding] - Cenarion Expedition Honored Reputation
[Nature Armor Kit]x4 - Leatherworking
Crafting Totals
104 Eternium Ore, 156 Fel Iron Ore, 3 Primal Nether, 46 Primal Life, 64 Primal Shadow, 5 Primal Earth, 20 Adamantite Powder, 16 Heavy Knothide Leather
Resistance Gear (Shadow, Mother Shahraz) [Shadesteel Greaves] - Blacksmithing - Ashtongue Deathsworn Honored Reputation
[Shadesteel Sabots] - Blacksmithing - Ashtongue Deathsworn Honored Reputation
[Shadesteel Girdle] - Blacksmithing - Ashtongue Deathsworn Friendly Reputation
[Shadesteel Bracers] - Blacksmithing - Ashtongue Deathsworn Friendly Reputation
[Night's End] - Tailoring - Ashtongue Deathsworn Honored Reputation
[Blessed Medallion of Karabor] - "A Distraction for Akama" Quest Reward
Crafting Totals
9 Heart of Darkness, 5 Void Crystal, 28 Adamantite Bar, 18 Primal Shadow, 13 Primal Life, 1 Bolt of Imbued Netherweave
Resistance Gear (Fire, Illidan) [Inferno Tempered Chestguard] - G'eras - 30 Badges
[Inferno Tempered Leggings] - G'eras - 30 Badges
[Inferno Tempered Boots] - G'eras - 20 Badges
[Inferno Tempered Gauntlets] - G'eras - 20 Badges
[Flamebane Helm] - Blacksmithing - Aldor Exalted Reputation
[Lesser Arcanum of Resilience] - Libram Quest Reward
[Glyph of Fire Warding] - Honor Hold or Thrallmar Honored Reputation
[Flame Armor Kit]x2 - Leatherworking
Crafting Totals
12 Fel Iron Bar, 9 Primal Water, 3 Primal Fire, 4 Heavy Knothide Leather, 1 Libram of Resilience (Requires: 1 Black Diamond, 4 Crystal Spire, 1 Burning Essence)
Optional Replacements
There are several options for Fire Resistance gearing thanks to a crafted Blacksmith set. One particular trade-off, depending on available Defense/Resilience gear, is that it can be more beneficial to socket
[Flamebane Gloves] for Resilience than using the badge-bought gear. Here is a list of valuable replacements to consider when putting a set together.
[The Fel Barrier] - Nexus-Prince Shaffar (Heroic Mana-Tombs)
[Flamebane Gloves] - Blacksmithing - Aldor Honored Reputation
[Flamebane Bracers] - Blacksmithing - Aldor Friendly Reputation
[Flamebane Breastplate] - Blacksmithing - Aldor Revered Reputation
[Formula: Enchant Cloak - Greater Fire Resistance] - Enchanting - Cenarion Circle Friendly Reputation
Mechanical Implementation (Theory)
Blizzard has explicitly detailed the mechanical implementation of Spell Resistances. The following is pulled from their
Resistances page:
When hit by a spell, you have two chances to resist the spell. The first chance is based on your level. If you are much higher level than the attacking caster, you will have a significant chance to resist the caster's spell, but if you are much lower level, you will have a minimal chance to resist the spell (minimum of 1%). If you make this resistance chance, you are completely unaffected by the spell.
The second chance to resist is based on your resistance score and the level of the caster. The higher your resistance score in relation to the level of the attacking caster, the higher your average resistance percentage, up to a maximum of 75%. Against most spells, this resistance percentage is the straight % chance to completely resist the spell. Against direct-damage spells (spells that deliver their full damage upon impact, such as Fireball, Mind Blast, and Earth Shock), this resistance is the percentage of damage you will resist on average.
When hit by a spell, you have two chances to resist the spell. The first chance is based on your level. If you are much higher level than the attacking caster, you will have a significant chance to resist the caster's spell, but if you are much lower level, you will have a minimal chance to resist the spell (minimum of 1%). If you make this resistance chance, you are completely unaffected by the spell.
When you are hit by a direct-damage spell, you have a chance to resist 100%, 75%, 50%, 25%, or 0% of the spell's damage, depending on your resistance score in relation to the level of the attacking caster. Your average percentage of damage resisted is the weighted average of your resistance percentages for each level of damage resistance (100%, 75%, 50%, 25%, and 0%). Using, as an example, a fire resistance score of 250 vs. a level-50 mage's fire spell, you would on average resist roughly 75% of the damage of that spell (as can be deduced by calculating the weighted average for the corresponding column in the example table below). To further the example, if you had fire resistance of 100, you would, on average, resist roughly 30% of the spell's damage. |
Sources
Hydross gear set lists I worked with were originally posted on Wowhead by Immortares (WoW-EU Twisting Nether).