Glory of the Icecrown Raider (25 player)

These achievements are account wide, you can use any character to do them. You can go through and do all the achievements and go back to finish "Once Bitten, Twice Shy" on a different character.

So in this case having multiple 100's is very beneficial!
YOU CAN DO ALL OF THE ACHIEVEMENTS LISTED ON NORMAL 25 PLAYER, KEEP IN MIND THE ACHIEVMENTS THAT SAY "HEROIC" IN FRONT OF THEM WILL HAVE TO BE COMPLETED IN HEROIC MODE 25 PLAYER.

Please up vote this, more people need this information, I know I did!

Boned - Do not get impaled with an ice spike for more than 8 seconds (kill Lord Marrowgar as fast as you can)
I'm on a Boat - Each player can only visit the enemy gunship once
Dances with Oozes - Kill Rotface without a Big Ooze casting Unstable ooze explosion
Nausea, Heartburn, Indigestion... - Kill Professor Putricide without using Regurgitated Ooze on the Abomination (Kill Professor Putricide as fast as you can)
Once Bitten, Twice Shy - Defeat Blood-Queen Lana'thel as a vampire then again without becoming a vampire (to become a vampire you must be the only one attacking Blood-Queen Lana'thel the rest of your team must stand back and not attack; to not become a vampire you must stand back and let someone else attack or if you are soloing, kill Blood-Queen Lana'thel as fast as you can)
All You can Eat - Kill Sindragosa without any member of your team getting more than 5 stacks of Mystic Buffet (kill Sindragosa as fast as you can)
Neck-Deep in Vile - Kill every Vile Spirit that spawns before it explodes and then defeat the Lich King
Full House - Kill Lady Deathwhisper with at least five different types of Cultists active at the time of her demise (do not knock her HP below 80% if she enters the second phase she will no longer change the cultists into the ones you need. You can kill every add that is sitting in front of her once you start attacking the ones you need will spawn, once they do you only need to keep one of each alive. After they all spawn take them right beside Lady Deathwhisper and she will turn them into the following: Cult Fanatic, Deformed Fanatic, Reanimated Fanatic, Cult Adherent, Reanimated Adherent. After all these are present you can kill Lady Deathwhisper, DO NOT USE AOE or the adds will die and you will not get the achievement.)
I've Gone and Made a Mess - Kill the Deathbringer before the Mark of the Fallen Champion is cast 5 times (Kill Deathbringer as fast as you can)
Flu Shot Shortage - Kill Festergut while no one on your team ever had 3 stack of Inoculated (Kill Festergut as fast as you can)
The Orb Whisperer - Kill the Blood Council without anyone on your team taking more than 25,000 spell damage in a single hit (kill the Blood Council as fast as you can)
Portal Jockey - Enter every portal spawned by Valithria Dreamwalker before healing her to full health (What I did was healed Valithria Dreamwalker before ANY portals appeared and got the achievement, make sure to kill the adds attacking Valithria Dreamwalker or the heals with take longer. These achievements are account wide so if you jump on your healer to complete this it will count for every character you have)
Been Waiting a Long Time for This - Allow Necrotic Plague to stack to 30 before defeating the Lich King (30 stacks does not need to solely be on ONE person, if there are 5 on an add or your teammate and 25 on you that is considered 30 stacks, and once the stacks hit 30 and if they go away that is STILL 30 stacks and you will still get the achievement. Once you hit 30 stacks knock the Lich King down to 70% he will transition to the middle of the platform and start a stormy looking thing on the ground and there will be targets that will come after you that knock you back and can knock you off so either: Stand at the bottom of the steps facing away from them OR stand next to the Lich King and make sure to kill those targets before they get to you. Once you get to this stage you must knock the Lich King down to 10% HP and NO LOWER, let him speak, he talks forever but make sure he is done, when he is, kill him; if you die when he starts his speech do NOT release you will be resurrected once he is finished talking then you can kill him this will only happen if you die AFTER or right as he begins his speech and you get your achievement.)

These are the same in 10 player mode

<NAME>,

As the Lich King's influence wanes, some of his more powerful minions have wrested free of his grasp.

This frost wyrm drake my men captured is a prime example. She has a will of her own and then some.

One of my men lost an arm breaking her in, but she now take to riders fairly well -- provided they themselves are skilled and strong willed.

Please accept this magnificent beast as a gift from the Knights of the Ebon Blade. It was an honor to fight along your side in this greatest of battles.

With honor,
Darion Mograine

Rewards Reins of the Icebound Frostbrood Vanquisher. A whitish coloured Armoured Frostwyrm mount that flies at 310%.