T17 Pre-Pull Gear [Pre-Patch]

Death Knight

(2) Set (Unholy): Your pet deals 120% additional damage while Dark Transformation is active.

This evidently will give your pets 320% more damage, and yourself 10% more damage / 15% quicker attacking, on pull.
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Hunter

(4) Set (Marksmanship): While Trueshot is active, your critical strike damage increases by 3% per second.

This evidently will give you 40% haste, and ~42% – 45% critical strike on an attack before the ring explodes.

(4) set (Beast Mastery): While Bestial Wrath is active, one additional pet is summoned to fight with you.

This evidently will give you, and your pets 20% more damage- and two pets to use. When combined with Stampede, this will give you 6? 7? pets, for a total of 120%-140% more damage on pets.

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Rogue

(2) Set (Subtlety): When you activate Shadow Dance, you gain 5 Energy every second.
(4) Set (Subtlety): When Shadow Dance expires, your next finishing move refunds 2 combo points.

This evidently allows you to use stealth abilities / gain the benefit of stealth for the next 3 seconds- while gaining a net 15 Energy / getting back 2 combo points.

Sublety is worthless as a spec at the moment, so this isn’t good anyways. Good to mention though, as Blizzard is still tuning stuff until Legion based on current DPS / HPS ongoing.
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Warrior

(4) Set (Fury): While Battle Cry is active, your attack speed and critical strike chance increase by 6% every second.

Evidently this will increase your critical strike by 100%, and give you a 6% … 30% quicker attack speed / critical strike chance for the first 5s of your burn.