Festergut Strategy Ideas
Fester is a huge DPS check (and a huge tub of greasy, gassy, gopher guts), but even if we have the dps to kill him, we will never make it through the fight if everyone isn't working with the mechanics to ensure they stay alive.
This is something I've put together after having seen this fight in several different raids. As always, Sbin is the raid leader. If anything in this guide runs counter to his experience or ideas, I defer to him for the final execution in the raid. This guide involves using a static rally point to which all ranged must run during spores; it's also valid to have everyone run wherever the spore pops in the ranged group. Right now, I can't remember which one we've been doing. 
Also, please help me correct anything I have misstated or made unclear, or that you would like to add. Writing out the Spore Movement Priority System⢠makes it look very confusing, but it's more just being aware of what your own role is and who else has the spores at any given time. Oh, and apologies for wall o' text.
General Stuff
It's a cyclical 1-phase fight with a 5 minute enrage timer. There really are not that many things you need to watch, but it's imperative that you do pay attention to those things.
Seven to eight people must remain at range. This does not mean absolute maximum range, it just means out of melee, plus give it a safety distance. These people will be targets of Vile Gas, causing disorientation and damage. They must be spread out 8-10 yards apart to prevent the gas from spreading to other players. If a healer must be in this group, make it a raid healer, not a tank healer.
Everyone else can smash in behind Fester. He has a very small hitbox, but has no frontal aoe damage abilities like Cleave.
Healing Issues: The cycle of damage
The room-wide [spell]Gaseous Blight[/spell] starts out around 4500 damage every 2 seconds to the whole raid. When Fester does his first [spell]Inhaled Blight[/spell], the raid-wide damage drops to 3000, but he is now hitting the tank 30% faster and 30% harder. Second inhale, raid damage drops again to 2000 per tick, and he starts hitting the tank 60% faster and harder. Third inhale, raid damage is now only 1500 but
he's hitting the tank 90% harder and faster. Raid healers should slowly shift to tank healing as the inhales go up. ((Damage per tick of Gaseous Blight may not be correct, as there's disagreement from various sources, but the proportions should be close))
Note that
raid damage will spike for 6 seconds during [spell]Gas Spore[/spell], as (hopefully) everyone will have the [spell]Blighted Spores[/spell] DoT,
and will spike for 2-3 people at other times due to
Vile Gas.
The tank stuck facing Fester at +90% damage needs to blow cooldowns at this point. Shields, paladin talents and anything else someone can do to mitigate tank damage is really necessary here. Tanks will know what their options are much more than I. This tank-smashing phase lasts around 30 seconds.
30 seconds after the third inhale, Festergut will "equalize" and release all that gas back out in [spell]Pungent Blight[/spell]. This will hit the whole raid for a ton of shadow damage.
You will die if you do not have at least 1 stack of [spell]Inoculated[/spell] plus at least 38000 hp, and you'll probably die to Gaseous Blight right afterward if you don't have at least 2.
3 stacks is the ideal for 25 man. If you only have 2 stacks, be ready to bubble, iceblock, AMS, or use any other damage-mitigating ability you have during the 3 second cast in order to live through it. Gaseous Blight now starts up again at 4500 per tick, and the cycle repeats.
Gas Spores. Great News, Everyone! This Will Only Sting A Little!
Every 25 seconds or so Fester will cast three Gas Spores randomly on three raid members. With the mods most of us are running, this should put a symbol over the targeted players' heads.
EVERYONE must collapse on top of someone with a spore. You HAVE to watch for this ability and get yourself to the spore, which lasts 12 seconds. There's
only about a 5 yard range on the spore debuff, so you need to be very close to the person with it. After 12 seconds, the spore will explode and give you a DoT, [spell]Blighted Spores[/spell], which lasts 6 seconds, doing damage every second. After the DoT wears off, you will have a stack of [spell]Inoculated[/spell]. Three stacks of Inoculated later, Pungent Blight goes off and the process begins again.
Vile Gas is not cast during this portion, so ranged may safely clump up until they get the DoT. After you get the DoT, move immediately back to your original spot.
Warning: i
f two spores are close together, everyone in range of both will get a double stack of the dot. It's not an immediate wipe, but raid healers have quite enough to do without adding a sizable chunk of completely avoidable damage.
The only slightly tricky thing is when two or three spores spawn in melee, or all three spores spawn at range. All that is needed is a tiny bit of common sense here. Lemme break it down.
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3 spores in melee. If one is on the tank, that is the melee spore.
ALL melee group MUST move forward under Fester's legs in order to be in range of the spore. He won't hit you. Just get close to the tank. The other 2 melee spores must move immediately out of the group. If you are a healer, just get out of melee range. Any ranged folks near you can move to you. If you are DPS, shake a leg immediately to the ranged rally point, say, the door. All ranged collapse on the door. When the spore explodes and DoT icon comes up, move immediately back to your assigned positions. If for some reason 2 healers get the spores in melee, raid healers move to rally point, tank healer just gets out of range of everyone else. If the tank is not a spore, Skull stays, X hits the rally point, Square moves out and stands alone. Just know who you are and what your role is, and it's easy to get it done.
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3 spores at range. Square moves directly under Festergut's, um, distinct lack of naughty bits. Melee squishes in close. Skull goes to rally point. X stays put unless you're too close, then just move away a bit. Ranged collapse on rally point, or whichever spore happens to be closest to you. Wait for DoT, then immediately return to positions.
Do not cut through the melee group at this time, or you may lose the minimum number required to be at range. If Vile Gas hits the melee stack, we wipe.
Priority list for spore moving: DPS>Raid Heals>Tank Heals. If you are a DPS, look around and see who got the other spores. Likely you will be moving if there's another spore close to you. But it's a DPS race, you say? Dead tank = wipe, no matter how much DPS you put out in the 15 seconds you were able to stay on the boss instead of running out.
If 2 DPS have spores, lowest mark moves: i.e., Skull always stays, X moves if other is Skull, Square always moves. (We can also just split the raid into tanks and non-tanks, and go by Mark to determine who moves. I've just seen tanks die during this section because the healer had to run. This is probably more of an issue in 10 man.)
That's about the extent of it. As Phoronid pointed out, the
average raid dps needs to be around 7200 in order to beat the enrage timer. You must bring your A-Game to this fight. It's not something you can be carried through with subpar gear, spec, game awareness, and button mashing skills.
Tips:
⢠Have the top ranged dps stand at the ranged spore rally point, so they can dps without stopping. Or if a tank healer must stay at range, have them be the rally point. Otherwise have any ranged healers line up on either side of the rally point, so they won't have to move far.
⢠If you are in the melee stack and don't know if you have the spore, move or strafe slightly every time a spore comes up in melee. If it moves with you, it's on you.
⢠Watch your debuffs for the purple icon Blighted Spores. This is the lead-in DoT to Inoculation. As soon as you see that icon, run back to your assigned position.
⢠Count your stacks of Inoculation. If the room is clear (no orange gas in it) and you only have 1 or 2 stacks, get ready to use your damage mitigation shortly.
⢠Mages can Iceblock and Shadow Priests can use Dispersion through Pungent Blight if they would prefer to completely ignore spores and not move. Vanish works too, if cast exactly as the Blight cast ends.
⢠Pally bubble and DK Anti-Magic Shield will pop the Blighted Spores dot, but you will NOT get the stack of Inoculation. Just let the DoT tick.
⢠Healers can /focus Festergut to see how many stacks of Inhaled Blight he has. Or watch your target of target window for buffs.
⢠Hand of Salvation on the tank switch, so the one with 8-9 stacks of Gastric Bloat doesn't pull aggro back and blow the raid up.
⢠Don't TotT or MD the tank to dump your threat without checking his Bloat stack first.
⢠Tanks should try to DPS as hard as possible when they are not tanking. +80% or more damage should help you out a bit at least.
⢠Can have a plate dps or a bear tank Fester on the pull to snag 1-2 stacks of Bloat, giving them increased damage for 100 seconds. Not sure how this would affect the timing of Bloat switching vs Pungent Blight, but I know it's done. Probably would just swap tanks 1-2 stacks early.
Sources: Bosskillers, Wowwiki, Wowhead, plus random Google search results and wins & wipes on two characters in two sizes of raid.