New expansion 'Wrath of the Lich King' information.

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Blizzards official page states the following;

Master the necromantic powers of the Death Knight - World of Warcraft's first Hero class.

Quest to level 80, gaining potent new abilities and talents along the way.

Learn the craft of spell augmentation with the new Inscription profession.

Brave the harsh new continent of Northrend, the icy domain of the Lich King.

Engage in epic siege warfare, deploying mighty siege engines to lay waste to destructible buildings in your path.

Transform your hero's look with new character-customization options, including new hairstyles and dances.

Explore perilous new dungeons filled with some of the deadliest creatures -- and greatest treasures -- on Azeroth.

Hero classes are finally being announced in the game, which is something most people wanted from day one.

Originally Posted by blizzard

August 3, 2007
World of Warcraft: Wrath of the Lich King announced!
Blizzard is proud to officially announce the next World of Warcraft expansion set, World of Warcraft: Wrath of the Lich King! With the opening of the Dark Portal, and the renewed war to stop the Burning Crusade's destruction of worlds, the heroes of Azeroth have given little thought to the frozen wastes of Northrend – and the terrible, ancient powers that wait there. Yet the brooding evils of the fallen Nerubian empire and their malevolent sovereign have not forgotten Azeroth...

World of Warcraft: Wrath of the Lich King™ will open the forbidding wasteland of Northrend to exploration by the hardiest adventurers. New levels of power, challenging new dungeons and encounters, an exciting new character profession, and the game's first hero class are just some of the new features awaiting players in Wrath of the Lich King.

Their official press release on it.

From the General Forums dealin with the Death Knights :

Here's a list of everything we know for sure about Death Knights.

A "Hero Class" unlocked by completing a quest chain at 80.

Any character/class may complete the quest chain and unlock the Death Knight.

The quest will not require raiding, and has been likened to the Warlock quest for the Epic mount.

Once unlocked, the Death Knight may be rolled as any other class, with the stipulation that Death Knights will be begin at a high level. It has not been decided what level, but it will be somewhere between 55-70.

Designed to fufill the roles of Tanking or DPS.

A melee spell caster class.

Wears plate, and wields 2H or DW swords and axes. No shields.

Will not use Rage, Mana, or Energy.

Instead utilizing an entirely unique "Rune" system, inwhich a Death Knight will use some combonation of 6 Blood, Unholy, or Frost runes to unleash thier abilities and spells.

Runes will be used up incombat, but may be carved onto the Death Knight's weapon at any time outside combat.

Of the few Death Knight spells unvield, some have the ability to transform a percentage of healing an enemy target recieves into damage.

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