ok , i know this doesn't belong here but .... 1. I can't post in Boss Raid Encounter forum & 2. Skelnik is lazy on updates >.<
FYI , this is not something i made up , i just copy & pasted from reliable sources ... mainly Bosskillers and Tank spot. I'll focus more on the 25man for this strat guide.
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An appropriately geared raid for this instance will have spent some time gathering equipment in the first wing of Icecrown Citadel. You will want most of your raid members to have a majority of item level 245+ gear for the 25 man version, and 232+ for the 10 man version. In general, the same group of players that beat the first four bosses in this instance should be geared enough to attempt this encounter.
Raid Composition
25 man
2 tanks - This encounter requires two tanks to rotate tanking Festergut throughout.
4-6 healers - Your raid will want at least 2-3 good tank healers, and 2-3 solid raid healers. However, all of these healers should be fairly flexible in their role, as the amount of damage taken by both the MT and the raid will vary widely over the course of the encounter, making it necessary to adjust healing to compensate. Take the minimum number of healers needed, in order to make room for more DPS so that your raid is safe from Festergut's berserk timer.
17-18 DPS - There are no particular skills such as interrupt/CC/etc. needed in this fight, so any DPS will do as long as they are adept at moving quickly when needed while maintaining good damage output.
ATM , we struggle with keeping tanks up and not losing too many dps ... 6 healers are our best bet. If we get to a point were we wipe at 3% then we might switch 1 healer for an additional DPS.
Mobs and Abilities
Festergut : 40.3 HP million HP in 25 man
Festergut will melee swing for 11-13k in 10 man and 17-19k in 25 man, assuming he has no stacks of Inhaled Blight and is hitting a properly geared tank.
Gastric Bloat - This is an ability used every ~15 seconds on the current tank, which deals a spike of nature damage and leaves a 100 second debuff on the tank. This debuff increases the tank's damage done by 10%, and can stack up to 10. However, if it hits 10 stacks, it causes Gastric Explosion.
Gastric Explosion - This ability only happens if the Gastric Bloat stack on the tank is allowed to reach 10 stacks. If that happens, the tank will explode, dying instantly and dealing a very large amount of nature damage to all other players in the room (probably killing them as well). Don't let this happen, or it will be a wipe!
Gaseous Blight - this is a room-wide layer of orange-brown gas on the floor. It will cause all players standing in it to take ticks of shadow damage every few seconds. It starts off 4 layers thick, and each time Festergut inhales a layer of it, the animation will get lighter and the ticks of damage on the raid will get smaller. He will inhale 3 layers before exhaling it all back into the room and then starting the process over.
Inhale Blight - This is a 3.5 second cast uninterruptable ability used by Festergut every ~30-35 seconds. It has a 30 second cooldown. Each time he uses it, a layer of the Gaseous Blight is removed from the room, and he gains a stack of Inhaled Blight, increasing all his attack speed and physical damage done by 30%
Inhaled Blight - This is the buff that Festergut gains when he uses Inhale Blight. It stacks to three, and lasts until he exhales. Each stack increases Festergut's attack speed and physical damage done by 30%. Healers and the tank should all be aware of how many stacks Festergut has, and use protective cooldowns accordingly as he starts hitting harder.
Vile Gas - This is an instant cast ability that Festergut will use on random raid members (1 at a time in 10 man, 2-3 at a time in 25 man) every ~10-15 seconds. The afflicted player will take a hit of nature damage, be disoriented, and animate like they are vomiting for 6 seconds. During these 6 seconds, the victim and any other players within 8 yards of the victim will take ticks of nature damage every 2 seconds. Have all ranged players spread out to minimize raid damage from this ability. It doesn't appear to be used on melee as long as there are enough players at range (similar to General Vezax's Shadow Crash ability mechanics). The lower limit seems to be 4 ranged players in 10 and 8 in the 25 man version.
Gas Spore (boss ability) - This is an instant cast ability that Festergut will use every ~25 seconds. Each time he uses it, two random raid members (3 in 25 man) will be hit, giving them the Gas Spore debuff. There will be a spore animation floating above the heads of the players hit. All other players should run to one of the people with this animation, getting within 5 yards of them before 12 seconds is up, in order to receive a stack of Innoculated.
Gas Spore (player debuff) - This is the debuff that appears on the players hit by Festergut's Gas Spore. It lasts for 12 seconds, at the end of which the spore explodes, hitting all players in range (~5 yards) with Damage over Time ("DoT") effect called Blighted Spores. As soon as the Gas Spore explodes, all ranged players should spread back out to minimize damage from Vile Gas.
Blighted Spores - This is the DoT given to all players in range of a Gas Spore victim when the Gas Spore explodes. It ticks for shadow damage every second for 6 seconds, and then leaves behind a stack of Inoculated. Ideally, this will be hitting everyone in your raid at once, so healers should be aware and ready to keep everyone healed up.
Inoculated - This is the debuff left behind after Blighted Spores hits a player. It reduces shadow damage taken by 25% per stack, and can be stacked up to 3 times. The debuff lasts for 2 minutes, and gaining a second or third stack refreshes this duration.
Pungent Blight - This is a 3 second cast ability used by Festergut every 2 minutes or so. He will use it ~30 seconds after each time he gains a third stack of Inhaled Blight, and using it removes all of his stacks of Inhaled Blight. This ability will exhale all of the Gaseous Blight layers back into the room, and hit everyone in the raid for a very large amount of shadow damage. In order to not die outright, everyone will need at least one stack of Inoculated. Ideally, everyone in the raid will have 2-3 stacks of Inoculated, and the damage from Pungent Blight will be very manageable.
Strategy
Normal positioning
Gas Spore positioning
Rinse & repeat ! :)
I highlighted the nature damage part of the encounter , i'm still convinced Nature Aura Resist from a hunter or Nature Resist Totem from a shammy would lower the damage on the tanks/dps.