Yes, yes, we know you're curious about what the Ulduar boss encounters will be like, loyal readers. With 14 bosses, 11 hard modes, and an optional heroic boss, we wonder, too! We'll be able to test some of these encounters on the 3.1 PTR soon, but there are, of course, those of us who just can't wait to know anything about what's going on in Ulduar.
Luckily, ever-resourceful players and dataminers have acquired information about spells and abilities related to bosses in Ulduar from the 3.1 PTR files. There's a lot of of stuff in here -- some of it may make it into the live game, some may not, and some may be related to vehicles or other sundries involved with encounters. I'm going to go into detailed analysis of those encounters for which detailed spells exist.
It goes without saying that these will be huge spoilers to anyone who doesn't want their Ulduar experience to be anything but pure, so don't read past the jump if you don't want to know!
The datamined information comes from this thread on the official forums, with links to the appropriate spells on Thottbot.
Dominate Mind - Mind controls a target temporarily and reduces Sanity by 20.
Low Sanity Screen Effect - Just a visual.
Psychosis - 20000 Shadow damage and reduces 20 Sanity.
Sanity - 100 stacked buff, if it reaches 0 you are permanently mind controlled. One Sanity regenerates per 3 seconds.
Touch of Dominion - Subjugates the target to the will of Yogg-Saron, weakening it (-10% HP and damage), yet "conferring a subtle control". Appears to stack every 180 sec.
Yogg-Saron's fight appears to be a sanity-based encounter, and if you're not already thinking of Eternal Darkness, we're not friends. There's a sanity meter, a mind control/reduced effectiveness debuff, even a low sanity visual effect. Your sanity regenerates by one point every three seconds, and it ticks down as you engage him, take damage from him, or are temporarily mind-controlled. If it reaches zero, you're permanently under the thrall of Ol' Yoggy.
Flash Freeze - Freezes the target in a block of ice. Other spells mention that a frozen target hit by flash freeze dies instantly, and that it is in fact Hodir's ability.
Hodir's Fury - 15000 Frost damage and a 9 second stun to all enemies.
Shatter Chest - Most likely Hodir's loot mechanic.
Toasty Fire - Likely a player ability. Creates a fire which prevents the effects of Freeze and Biting Cold. Extinguished by "falling ice shards" or "powerful frost magic" - most likely Blizzard and Flash Freeze.
Blizzard - 1.5k (10), 3k (25) frost every 2 sec for 10 sec.
Biting Cold - A la Keristraza, only only "diminished" by movement, not removed.
Winter's Embrace - Absorbs 185k damage, and while active increases physical damage dealt by 100%.
Unsurprisingly, the Watcher of Winter encounter appears to be based on cold! In order to survive, you have to light fires to prevent your raid from succumbing to the Biting Cold debuff and freezing. Blizzard and Flash Freeze appear to put the fires out if they contact them. If you do end up getting frozen, Flash Freeze will instantly kill you.
"Reduces Freya's Attuned to Nature stacks by 25" (spells also exist for other amounts)
"The presence of Elder Brightleaf increases magic damage dealt by Freya and her Allies of Nature by 50%"
Freya Summon Chest - it would appear that we do not kill her. There are eight spells of the same name, presumably for various difficulties.
Ironbranch's Essence - Increases damage dealt by Allies of Nature by 50%.
Lifebinder's Gift - Summons an "Extraplanar Spore"
Stonebark's Essence - Increases physical damage dealt by Freya by 50%.
Summon Allies of Nature
Touch of Eonar - Heals Freya for 6000/s (10) or 24000/s (25).
It looks like Freya's fight is a straight-up Sartharion-style encounter. There are three Elders -- Brightleaf, Stonebark, and Ironbranch -- who will grant Freya powers if they're alive. The existence of 8 summoned chests confirms this, with each chest corresponding to a difficulty level on normal or Heroic. She likely summons in Allies of Nature a la Twilight Whelps, and the Attuned to Nature stack she has likely has to do with how we damage her.
Most of the other encounters only have bits and pieces of their spells so far. For those wondering about this -- I was! -- it looks like even though you fight him, Thorim might still help you after all.
Patch 3.1 brings us Ulduar, dual specs, significant changes to all the classes, and more! We've got you covered from top to bottom with our Guide to Patch 3.1.