The datamined information comes from this thread on the official forums, with links to the appropriate spells on Thottbot.

Yogg-Saron

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.

Preliminary analysis:
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.

Hodir

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%.

Preliminary analysis:
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.

Freya

“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).

Preliminary analysis:
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.

Main character Helcyon
Guild and server GM of Sanctuary (H) of Draka-US
Gaming and WoW background Previously played EverQuest. Started WoW in 2005 as Alliance on Icecrown; rerolled Horde on Draka in 2006. XPed most of levels 10-60 in Battlegrounds, becoming Draka’s first High Warlord. Has seen most PvE content except KJ in Sunwell and the original Naxxramas.

15 Minutes of Fame: Everyone knows that Achievements are time-gobblers. Where do you find your play time?
Helcyon: Lucky me, I am retired at 33. I play basketball, ultimate Frisbee and mountain bike and hike when I am not playing WoW. Outside of sports, my girlfriend and I like to eat out, since both of us are average cooks at best. If you are ever in Hawaii, I can tell you the best spots to dine and drink at, anything from the affordable to the hurt-your-bank-account meals.

As far as playing time goes, it varies depending on the week, I suppose. Two weeks ago, I played maybe seven to eight hours total. Some days, I just log in to check my auctions (because, well, all those WotLK mounts were expensive — and yes, I have every single one that could be purchased from a vendor, including the Hog!). On the current raid days, I am on at least six hours that day, minimum (about four for the raid and a bit before and after). If I get into any sort of Achievement or honor grind, I can spend three to four hours online very easily. When my girlfriend is free, I am … well … not allowed to play, unless she is in the mood to level her little Hunter (at which point we generally will spend 30 minutes to one hour playing together).

Of course, like any gaming freak, I do have my hot streaks of playing. Last year I broke my toe and was without sports for five months. The first few months of that I was online like a maniac. I am pretty sure I have clocked like 10 hours in a day before (lots of AFKs … but still …), and I have nights like last night where I can’t sleep, so I popped in a movie and then fished in Dalaran for four hours until I was tired enough to sleep.

I usually take my laptop with me when I travel, so I can WoW on the road as well. I think I have left behind my laptop only three times since I have started playing WoW. I usually take four to five trips a year, and a couple of those are just usually to an outer island.

You call your guild “casual,” yet you’ve covered almost all the content in the entire game. What does “casual” mean to you?
I guess the word casual is easy to toss around with the current content. I am pretty sure most guilds can clear all content in under 4.5 hours, for non-speed runs. Right now we have five or six days off a week from raiding 25-man content. We have always been a come-and-go guild, meaning we have never in the past enforced a kind of you need to make (random_01) amount of raids or be ( random_02) spec. We raided with what we had and adjusted to the fights accordingly. We raided an average of two to three days in TBC, and so far in WotLK it is about 4.5 hours of raiding per week, once we got the learning curve down.

So I guess “casual” to me is just being able to come and go as we please, not worrying about having to make our raids to force progression. I am confident that we will see most things, and though being a server first is always an awesome feeling, it is not something I am going to nerd rage over.

What is your guild currently working on?
Our guild is currently working on Sartharion + 3. We have come close; unfortunately, the last month we have been hit hard with our geared raiders being on vacation, exams in school, overworked or just having life changes at the moment. We are hoping for a good showing this upcoming week. It shouldn’t be an issue if we get the right folks online.

Are you and/or your guild doing much PvP now?
As far as PvP, our guild still does a good deal of it. In fact, we have a handful of players that only PvP. We had a few very high-ranked guild Arena teams this past season and even had a Gladiator. We do a few pre-made WSG groups weekly as a guild. I have not really tested the Arena system since the second season, as I was turned off by it. I have just about collected the needed gear to start my level 80 Arena campaign.

Honestly, I miss playing against guys on my own server. It was special. We had epic ABs and WSG matches against Alliance pre-mades during classic WoW days. I once had a 12-page jerk thread on the Draka forums because I wouldn’t allow anyone into my pre-made battles. A few of the HWLs that took rank after me (all Sanctuary) also had some jerk threads for similar reasons … never as long as mine, though! A lot of our old-school guys like to talk about the old-day PvP when it was all honor-based and still server only. Wintergrasp battles bring back some good memories, especially when I see an old rival, but it is not the same.

It sounds like you were a completist before the Achievement system ever came along. Had you already covered a lot of ground for the Achievements by your own oddball interests?
As I said previously, I had been working on my own oddball things prior to the Achievement system being put in place. I believed I was Exalted with most vanilla WoW factions like all Horde cities, Thorium Brotherhood, Timbermaw, etc.

What’s been the most difficult Achievement for you to earn so far?
The most difficult Achievement for me thus far has been Loremaster questing. It is not that it is difficult to complete, but I would prefer to be in WSG or AB Mind Blasting a Gnome.

Do your guildmates work toward most of these achievements with you, or is this pretty much a personal endeavor?
For the most part I have worked on Achievements alone. However, a group of us ran the Naxx-10 instance a few times to get all but the Spore Loser Achievement there. I was also for the most part able to keep the same group to complete all the heroic dungeon quests for my Red Proto-Drake.

We have a couple people with over 6,000 Achievement points in our guild. A few of us instance together when we can, but for the most part, we are off doing our own Achievements like professions or general or what-nots. I know I currently do not posses the most points on our server — but after taking the time leveling a couple of my alternate characters to 80, I feel I am catching up rather quickly.

Which of your titles do you typically choose to display over your head? Why?
The title I wear most often is High Warlord. You just can’t get it anymore and I was the server’s first, so it is special for me. I will occasionally wear other titles to goof around.

What Achievement did you most enjoy working toward? What was the most enjoyable process?
The Achievement I had the most fun getting was The Undying. I am pretty sure we were a server first there. The longer we would go on in Naxx without dying, the more intense each boss fight got. It made each fight that much more fun. I think when we made it to Kel’thuzad without anyone dying, I said I would guild kick the person that lost The Undying title for us. I was kidding of course … maybe … Luckily, we didn’t need to find out!

What achievement are you most proud of and why?
At this particular moment I am pretty proud of my Seeker Achievement (3,000 quests), but that is because quests and I don’t always get along. (My feelings about this Achievement) will probably change soon, though; I really never have felt that any particular achievement was that much more special than another.

What achievements are you actively working toward right now?
The Acheivement I just started pushing for is the 100,000 honorable kills. I am hoping to get it sometime in late March or early April. If I become blessed with a crazy amount of PvP time, I could get it as early as mid-March.

Is there an achievement you’re most interested in getting?
The Achievement I am most interested in getting is The Immortal from Heroic Naxx, just because I would like the title Helcyon the Immortal. We got through three wings before someone died recently. That was kind of a bummer. I thought we would have had it that particular evening.

Think you’ll get all the Achievements out there?
I don’t know if I will get every single Achievement out there. I do know that as long as I am playing WoW, I will be trying!