The 25 man version of Grand Widow Faerlina can be a daunting task, on top of the four worshippers in the 10 man version of this raid Faerlina has two Followers. These should be killed straight away, they have an AoE silence and will charge random raid members, something that can easily disrupt a raid.
In the 25 man version of Grand Widow Faerlina has around 6,760,000 and has some raid testing abilities which will ensure you raid's co-ordination is enough for the coming battles in Naxxramas. Some of Faerlina's abilities will really test your abilities, they are designed to cause widespread damage as well as some huge one target damage if you are not careful.
Grand Widow Faerlina's abilities in the 25 man version of Naxx are,
- Poison Bolt Volley - Faerlina's Poison Bolt Volley hits the closest ten players to Faerlina, it is used around every 15 seconds and deals 3300 to 4200 nature damage, as well as applying a dispellable DoT that does around 1900 to 2100 nature damage every 2 seconds for 8 seconds. Widows Embrace prevents the use of this for 30 seconds.
- Rain of Fire - Grand Widow Faerlina will cast her rain of fire spell repeatedly through the fight every 6 to 15 seconds. her rain of Fire spell has an 8 yard AoE radius and causes 3700 to 4300 fire damage every two seconds for six seconds.
- Frenzy - Faerlina's frenzy can easily break a raid group, she hits for 150% more, has a 50% melee haste increase and during this time will cause 20k damage. This must be dispelled ASAP with Widow's Embrace
Technically the followers can be tanked for the entire fight, however they charge random people and have an AoE silence. For this reason I suggest your group learns to take these two adds down in under 30 seconds.
All there really is to this fight is the co-ordination on the mind controls just as frenzy hits. You need to cause some major damage fast, but with a good raid group you should have no problem taking down the boss Grand Widow Faerlina!