So the next 5 man is going to be awesome, apparently you get to fight "memories" from a list of old bosses. The list so far (according to worldofraids.com) is...
Wrath of the Lich King
* Raid Bosses
o Algalon the Observer
o General Vezax
o Heigan the Unclean
o Ignis the Furnace Master
* Dungeon Bosses
o Cyanigosa
o Eck the Ferocious
o Ingvar the Plunderer
The Burning Crusade
* Raid Bosses
o Archimonde
o Entropius (M'uru)
o Gruul the Dragonkiller
o Illidan Stormrage
o Lady Vashj
o Prince Malchezaar
* Dungeon Bosses
o Priestess Delrissa
o Warlord Kalithresh
Classic WoW
* Raid Bosses
o Chromaggus
o Emperor Vek'nilash
o Hakkar
o Lucifron
o Onyxia
o Thunderaan
* Dungeon Bosses / Quest Targets
o Edwin VanCleef
o Herod
o Hogger
o Mutanus the Devourer
LOOK AT THE LAST FOUR, THAT'S JUST AWESOME!