WoW Tactics

We will be looking at both the 10 man and 25 man versions 

The 10-man version

• A Naxxramas-geared group should do fine with 2 tanks, 3 healers and 5 damage dealers. With better gear a healer might be replaced by a damage dealer.
• For some encounters a tank or healer might switch to damage spec. A good example of this is Hodir, where one frost resistance feral druid can tank both phases of the encounter.

The 25-man version

• Nearly full Naxxramas 25/Malygos 25 gear is highly recommended to start and absolutely required for the later encounters. Expect most encounters to require 6-7 healers for new groups. Three tanks are required for many of the encounters and some such as Thorim even benefit from a fourth tank.

There is a total of six sections through out this instance 

• The Siege of Ulduar,  this stage comprises of 4 bosses each of similar difficulty (however each with his/her or its unique qualities)

•  The Antechamber of Ulduar, This section of the instance contains 3 boss stages. If you count the three bosses you face at the begining there is a total of 5 (but the 3 at the start count as one encounter)