Blizzard's official comment about changes to stacking buffs in WOTLK. Comprehensive list of buffs inside.
Blizzard wall of text incoming.
EDIT: It's possible that this info has changed on the live servers now. If anyone has a link to a new updated list, please help me out. I don't want to have false info.
TLDR version: They want to allow people to not have to min/max so much and their solution is to make it really easy to fulfill all the raid's buffing and debuffing requirements. Everything is being designed around having abilities not stack as much for all classes. *It should be easier for an MB team to get all the synergies they could ever want from a smaller group*
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As Ghostcrawler has been posting recently, we've decided to make a change in the way we allow buffs and debuffs to stack exclusively in a raid. For the most part, what this change means is that many buffs and debuffs which were previously allowed to stack together no longer can, and that many buffs and debuffs which only a single talent specialization could bring can now be brought by multiple different specializations. The philosophy behind this change shows up in many of the changes we have made in Wrath of The Lich King, such as when we made almost all buffs raid-wide. We want players to be able to form raids and parties based on who they want to play with, rather than who has the correct talents and abilities to min-max their raid performance. Raid composition will still matter to some extent, but without this change, it would have overwhelmed every other aspect of raid planning (as we added new capabilities to each of 30 different talent trees). You no longer need to rigidly control the melee/spellcaster balance of your raid, or make sure every group has all the critical buffing classes, etc. This change has many class balance implications. Before we are done, we will thoroughly test the performance of every class. Do not assume that the classes' current performance relative to others in the beta is final. Some classes (and specializations) will need to be reduced in power and some increased. Many will complain the change has more impact on class X than class Y. We will address all those concerns via our internal testing and community feedback.
Ok, given that preamble, here is a comprehensive list of the changes which were made. If testers find additional changes not documented, or additional changes that need to be made ("Hey, buff XYZ got left out of the plan!"), please post and we will investigate.
There are thirty or so different categories buffs and debuffs fit into, and I will list each category and which spells/talents are in that category.
Armor Debuff (Major): Acid Spit (exotic Hunter pet), Expose Armor, Sunder Armor
Armor Debuff (Minor): Faerie Fire, Sting (Hunter pet), Curse of Recklessness
Physical Vulnerability Debuff: Blood Frenzy, (2nd Talent Spec TBA)
Melee Haste Buff: Improved Icy Talons, Windfury Totem
Melee Critical Strike Chance Buff: Leader of the Pack, Rampage
Attack Power Buff (Flat Add): Battle Shout, Blessing of Might
Attack Power Buff (Multiplier): Abomination's Might, Trueshot Aura, Unleashed Rage
Ranged Attack Power Buff: Hunter's Mark (only Hunters benefit, so no need to exclude against other class abilities)
Bleed Damage Increase Debuff: Mangle, Trauma
Spell Haste Buff: Wrath of Air Totem
Spell Critical Strike Chance Buff: Moonkin Aura, Elemental Oath
Spell Critical Strike Chance Debuff: Improved Scorch, Winter's Chill
Increased Spell Damage Taken Debuff: Ebon Plaguebringer, Earth and Moon, Curse of the Elements
Increased Spell Power Buff: Focus Magic, Improved Divine Spirit, Flametongue Totem, Totem of Wrath, Demonic Pact
Increased Spell Hit Chance Taken Debuff: Improved Faerie Fire, Misery
Percentage Haste Increase (All Types): Improved Moonkin Aura, Swift Retribution
Percentage Damage Increase: Ferocious Inspiration, Sanctified Retribution
Critical Strike Chance Taken Debuff (All types): Heart of the Crusader, Totem of Wrath
Melee Attack Speed Slow Debuff: Icy Touch, Infected Wounds, Judgements of the Just, Thunderclap
Melee Hit Chance Reduction Debuff: Insect Swarm, Scorpid Sting
Healing Debuff: Wound Poison, Aimed Shot, Mortal Strike, Furious Attacks
Attack Power Debuff: Demoralizing Roar, Curse of Weakness, Demoralizing Shout
Stat Multiplier Buff: Blessing of Kings
Stat Add Buff: Mark of the Wild
Agility and Strength Buff: Strength of Earth Totem, Horn of Winter
Stamina Buff: Power Word: Fortitude
Health Buff: Commanding Shout, Blood Pact
Intellect Buff: Arcane Intellect, Fel Intelligence
Spirit Buff: Divine Spirit, Fel Intelligence
Damage Reduction Percentage Buff: Grace, Blessing of Sanctuary
Percentage Increase Healing Received Buff: Tree of Life, Improved Devotion Aura
Armor Increase Percentage Buff: Inspiration, Ancestral Healing
Cast Speed Slow: Curse of Tongues, Slow, Mind-numbing Poison.
In each category, you can only benefit from the most powerful spell granting that effect. For example, Fel Intelligence grants Spirit and Intellect, both weaker than Arcane Intellect and Divine Spirit. If a player has Fel Intelligence and receives a stronger Arcane Intellect buff, he will gain the intellect value from Arcane Intellect and the Spirit value from Fel Intelligence.
In most cases, fully-talented players will have exactly equal power on the strength of these buffs and debuffs. Fel Intelligence is an example of where one ability is weaker than others. The buffs in the "Increased Spell Power Buff" category are also not all the same potency, as they scale in grow in radically different ways. In virtually every other case, however, the buffs are equal. This means, for example, that fully-talented Battle Shout and Blessing of Might now grant the exact same amount of Attack Power.
In addition to this change, we also needed to address the "mana battery" roles in a raid. The mana regeneration effect they grant is no longer limited to their own party, and it no longer depends on the amount of damage they deal. Each time they trigger the mana regeneration effect, 10 people in their raid group will receive a buff which causes them to regenerate 0.5% of their maximum mana each second. This buff, Replenishment, will be given preferentially to raid members with the lowest mana, but will re-evaluate which raid members receive it each time it is fired. Replenishment is provided by Shadow Priests, Survival Hunters, and Retribution Paladins.
Finally, we have modified Heroism and Bloodlust to affect the entire raid. However, all affected raid members will be unable to cast or benefit from Bloodlust/Heroism for 5 minutes.
I will also list the changes to abilities which exhibit new behavior regardless of the exclusive categories. The changes usually mean the old behavior was removed and replaced by the new behavior. Numbers listed are for maximally-talented versions. Here is that changelist:
Improved Scorch: Increases spell critical strike chance against the target.
Winter's Chill: Also increases spell critical strike chance against the target.
Elemental Oath: Grants 5% spell crital strike to raid members.
Improved Moonkin Aura: Grants 3% haste of all types.
Earth and Moon: Increases spell damage taken from all schools by 13% on the target.
Misery: Causes spells cast at the target to have +3% spell hit.
Shadow Weaving: Buffs only self.
Improved Shadow Bolt: Buffs only self.
Expose Weakness: Buffs only self.
Shadow Embrace: Buffs only self.
Blood Pact: Grants health instead of Stamina.
Fel Intelligence: Has replacement ranks that grant flat values of Intellect and Spirit.
Frost Aura: Excludes properly against all other resistance buffs.
Grace: Reduces damage taken by target by 3%.
Rampage: Increases melee and ranged critical strike chance by 5% for the raid.
Improved Faerie Fire: No longer benefits melee and ranged hit chance, only spell hit.
Hunter's Mark: No longer increases attack power bonus from attacks against the target.
Improved Hunter's Mark: No longer grants melee attack power.
Sting (Hunter pet): Now acts as a minor armor debuff.
Waylay: Attack speed reduction changed to 20%.
Icy Touch: Only slows melee attack speed (not ranged or spell).
Tree of Life: No longer grants healing based on spirit, grants 3% increased healing received to raid.
Demonic Pact: Now buffs raid instead of debuffing monsters.
Focus Magic: Now buffs raid instead of debuffing monsters.
Totem of Wrath: Now grants a flat amount of spell damage, and all enemies in its radius have an increased chance of being struck by criticals.
Heroism: Cannot be recast while caster has Exhausted debuff, and those with Exhausted debuff cannot be affected by it.
Bloodlust: Cannot be recast while caster has Sated debuff, and those with Sated debuff cannot be affected by it.
Vampiric Touch: Grants Replenishment mana regeneration buff to up to 10 raid members on dealing damage.
Hunting Party: Grants Replenishment mana regeneration buff to up to 10 raid members on specified shots.
Judgements of the Wise: Grants Replenishment mana regeneration buff to up to 10 raid members on Judging.
