The following support gems are recommendations by GGG as listed in-game, and do not necessarily reflect optimal combinations or the views of the wiki.
Gem tier
Support gems
I
Cold AttunementCold AttunementSupport, Attack, Cold Category: Cold Attunement Tier: 1Support Requirements: +5 IntSupports Attacks, causing them to GainCold Damage but deal less Fire and Lightning Damage.Supported AttacksGain 25% of Damage as extra Cold Damage Supported Attacks deal 50% less Fire and Lightning DamagePlace into a Skill's Support Gem socket in the Skills Panel to apply its effects to that Skill. You cannot have multiple Support Gems of the same Category socketed within one Skill.
LeverageLeverageSupport Category: LeverageSupport Requirements: +5 DexSupports Skills which Hit Enemies. Supported Skills gain increased chance to Critically Hit against Immobilised Enemies.Supported Skills have 50% increased Critical Hit Chance against Immobilised EnemiesPlace into a Skill's Support Gem socket in the Skills Panel to apply its effects to that Skill. You cannot have multiple Support Gems of the same Category socketed within one Skill.
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II
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Cold PenetrationCold PenetrationSupport, Cold Category: Cold Penetration Tier: 2 Cost & Reservation Multiplier: 120%Support Requirements: +5 IntSupports any skill that Hits enemies, making those HitsPenetrate enemy Cold resistance.Supported Skills Penetrate 30% Cold ResistancePlace into a Skill's Support Gem socket in the Skills Panel to apply its effects to that Skill. You cannot have multiple Support Gems of the same Category socketed within one Skill.
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III
Cold ExposureCold ExposureSupport, Cold, Duration Category: Cold Exposure Tier: 4 Cost & Reservation Multiplier: 120%Support Requirements: +5 IntSupports any skill that Hits enemies, causing it to inflict Exposure when it Critically Hits an enemy.Supported Skills inflict Exposure for 8 seconds on Critical Hit with Cold DamagePlace into a Skill's Support Gem socket in the Skills Panel to apply its effects to that Skill. You cannot have multiple Support Gems of the same Category socketed within one Skill.
Elemental FocusElemental FocusSupport Category: Elemental Focus Tier: 3Support Requirements: +5 IntSupports any skill that Hits enemies, causing it to deal more Elemental Damage but be unable to inflict Elemental Ailments.Supported Skills deal 25% more Elemental Damage Supported Skills cannot inflict Elemental AilmentsPlace into a Skill's Support Gem socket in the Skills Panel to apply its effects to that Skill. You cannot have multiple Support Gems of the same Category socketed within one Skill.
Nimble ReloadNimble ReloadSupport, Ammunition, Projectile Category: Nimble Reload Tier: 4Support Requirements: +5 DexSupports CrossbowAmmunition Skills, causing them to Reload bolts significantly faster.Supported Skills have 60% increased Crossbow Reload SpeedPlace into a Skill's Support Gem socket in the Skills Panel to apply its effects to that Skill. You cannot have multiple Support Gems of the same Category socketed within one Skill.
Item acquisition
Hailstorm Rounds has restrictions on where or how it can drop.
Hailstorm Rounds: Bolts now fall in an expanding circle rather than overlapping with each other. Now has an Impact radius of 1 metre (previously 1.2), and a Rain radius of 4.0 metres (previously 2.5). One bolt now falls every 0.1 seconds (previously 0.3), and there is no longer a minimum distance the bolts can land from the firing location. Now deals 146-254% off Attack Damage at Gem levels 11-20 (previously 109-204%), and has 130-157% more Freeze Buildup. Ammunition now has 100% more reload speed (previously 50% less).
Many Skills have had their base damage and/or damage growth per level rebalanced. Most of these changes are not specifically mentioned below as the changes are too widespread.
The mana cost for all Attacks, Marks and Warcries has been reduced, most notably at higher Gem levels.