Tanking: Two tanks, swapping at 9 stacks of Gastric Bloat (do not let this reach 10 stacks or you’ll explode).
Tank damage past the second and third inhales can be very heavy, so keep your finger on the cooldown buttons, especially when Gas Spores have just gone out and when you’re about to taunt. A few seconds’ delay from healers swapping targets can kill you, so help them out with a CD.
Tank him in the middle of the room. The first tank should be able to do high DPS as well, since they will benefit from the Gastric Bloat buff and maybe Bloodlust.

Healing: Bring your normal complement of healers to this fight.
The key for healers is responding to the oscillating nature of the damage, changing framatically from raid-heavy to tank-heavy as time goes on, resetting after the Pungent Blight cast. Keep a minimum number of healers assigned to the tank and to the raid, and let the others float as the situation demands.
In normal mode healers can and should be standing in with the melee to minimise movement.

Buffs: Shadow Resistance is a huge help, and since Vile Gas is “Shadowstorm” (nature or shadow, depending on your lowest resistance) having Nature resistance up may help as well, if you have spare Shaman.

Key Debuffs:
Gastric Bloat
Inhaled Blight (Boss) – Increases his damage and attack speed by 30% per stack.
Gas Spore – Affects 3 random people on 25-man, 2 on 10-man, gives Inoculated.

Bloodlust: We tend to pop BL just after our first tank swap, so the former MT can benefit from it as well. Other deciding factors might be theamount of trouble your healers are having keeping up with damage, you might want to help them out.

HP: 43,230,000 (25N), 13,666,100 (10N)

Enrage: 5 minutes.

Festergut is a relatively uncomplicated fight on normal mode, although awareness of your position and buffs is important. He has a tight DPS requirement given the movement involved.
For the tanks however, there is little to no movement involved, and his position is relatively unimportant.

To avoid Vile Gas being cast on the melee you need at least 7 players (3 on 10-man) standing at range so ranged DPS, and healers as needed, should spread themselves out around the room, at least 10 yards apart to avoid chaining the Vile Gas (the chain range is 8 yards, the extra 2 is to prevent any splash damage since the victim wanders a bit with the debuff). Everyone else should be in melee range.

The main obvious mechanic in this fight is the orange Gaseous Blight covering the room. This does damage to the whole raid every 2 seconds (3k initially, falling to 1.5k on 25-man normal) and just needs to be healed through. Every 34 seconds he will Inhale Blight, reducing the damage the Blight does to the raid but increasing the damage he does to the tank (cooldowns are very useful if you’re tanking after the 3rd Inhale). This gets interesting at the point when the 4th Inhale would be, when he will cast Pungent Blight instead, dealing 50k (on 25-man, 44k on 10-man) shadow damage to the raid and resets both the Blight and the boss’s damage bonus.

To survive the Pungent Blight, you need to be Inoculated, which you get by standing within 8 yards of someone with Gas Spore when it explodes. There will be 2 at a time on 10-man and 3 on 25-man, and they are very visible as big orange spores on the players’ heads. When the Gas Spore debuff fades (after 12 seconds) the spores explode, putting Blighted Spores on anyone within 8 yards for 3k per second for 6 seconds (on 25-man normal, 2k on 10-man) and giving everyone who survives the DoT 25% (stacking) shadow resistance. Everyone needs at least 2 stacks of Inoculated, preferably 3, in order to survive (Hellscream’s Warsong and PW:S can help to prop up a player’s effective health though).
Ice Block and Dispersion are fine to get you through, meaning you are free to DPS and ignore spores for one phase. The damage is magical though, so HoP won’t save you.
Since Pungent Blight is pure shadow damage, it can also help, especially on heroic, to have a paladin Aura Mastery their Shadow Resistance Aura when this is due.

The best way to handle Spores is to have designated Spore muster points, one in melee and one at range. There is time to call someone one Vent to assign Spores to run to either melee or range, but in practice we simply let DBM do the hard work and have a standing rule that the Skull always runs to melee. Since DBM assigns marks in group order (i.e. the victims are sorted by group number and the Skull goes on the lowest group number, then the Cross, etc), if melee are in groups 1 and 2 the skull will typically end up on a melee anyway.
One big caveat is that because of the DoT, 2 Spores exploding on the same spot, especially at high raid damage times, has a good chance of killing people, so on 25-man the Spores at range should be 10 yards apart and if 2 melee get Spores one will absolutely have to run out.

The final mechanic Festergut uses is Vile Gas. This is cast on 3 players (on 25-man, 1 on 10-man), and will splash to anyone within 8 yards of them. Players affected will take 12k damage over 6 seconds, and will be incapacitated, running around in a small area and vomiting over players within 8 yards of them, also for 12k damage over 6 seconds. Ranged should be spread out to prevent any splashing time spent incapacitated and to reduce the damage taken. Multiple people being affected by this next to each other tends to lead pretty quickly to deaths, since both players are now taking 24k over 6 seconds, so this is to be avoided.

Heroic

• Putricide will periodically throw Malleable Goo down on a player. The splash has a 10-yard range, and the target is shown by a small green goo puddle on the floor. DBM is not able to spot this yet, it seems
• Healers should stay away from melee to prevent too much Goo going in their direction. Goo being cast on ranged is mostly harmless, it’s very disruptive to melee.
• 3 stacks of Inoculated is required without cooldowns or PW:S to survive the Pungent Blight, which now hits for 75k (on 25-man, 65k on 10-man)
• Beyond the third Inhale, tank damage is very high.
• Positioning is far more important. See below for the revised positioning scheme

Because of the Goo, and the additional damage going around in general, positioning is more important and slightly different than normal mode:

• Melee should start standing behind and to the left of Festergut’s left leg, at max hitbox range. When a Goo is thrown at them (or when a Goo is thrown at anyone, if you’re having trouble spotting Goo on melee) they should immediately run across to behind and to the right of the right leg, again at max hit box range. Being at max range helps prevent any splash hitting the melee if Goo is thrown at the tank.
• Ranged and healers should position themselves spread 10 yards apart on the far side of the side of the room from Putricide. People with faster reaction times or higher movement speed should be further from the designated Spore points (Mages and Warlocks are good choices, because they can move instantly). The MT healers should be assigned to stand on the Spore muster points so they can heal without moving as much as possible.

Spore positioning also needs to be quite precise, since everyone needs to get every Spore on them to survive the Pungent Blight reliably. In addition, one of the Spore clusters may need to move if the Goo is aimed at them, so they need to know where to move to stay together.

• Melee should move inwards slightly towards the Boss to ensure the tank gets the Spore buff too, and should dodge Goo as they usually do.
• Ranged should collapse to their assigned muster point, one each side of the virtual Putricide-Festergut line. We find it helpful to mark these with totems, but you can use marks on the heads of your tank healers, whatever works. If your group is targeted for Goo it needs to be spotted and called, and everyone needs to run together 12-15 yards (to account for stragglers or an off-centre Goo) to the right. Again, marking the backup point is handy, but if you can coordinate without this assistance then more power to you! I can’t emphasise enough how important it is to stay together, otherwise some people miss out on getting Inoculated and will need cooldowns to survive with only 2 stacks.