As with all of my guides, this is not intended to be a strategy for the whole raid. It is only intended for rogues and other melee dps classes.
Festergut, like Saurfang, is a very easy fight for rogues. Specifically, this is a dps test for your raid. Your job is generally going to be standing still going all-out on the boss. Therefore, this guide will be fairly short.
On the pull, plant yourself right behind him and go nuts. The fight will last no more than 5 minutes so you’ll get to use your 2-minute cooldown abilities twice. If everything goes well in the fight, the boss won’t move at all, and neither will you. Your raid needs to average about 5-6k dps per damage class (depending how many healers you have and what your tanks can do).
This fight has one interesting mechanic. You’ll notice that the room is filled with a haze when you start. Everyone takes damage from that. Festergut will inhale some of the gas, which reduces raid damage but makes him hit harder.
Every so often there will be gas spores that spawn (two on 10-man, three on 25-man). In about 10 seconds the spores will explode, but you don’t want to avoid them. Get close to them! When they explode, you take a small amount of damage but, more importantly, you get a stack of Inoculation. You really want that. You should get three stacks from the first three spore spawns.
During the fight, after Festergut has inhaled all of the gas in the room, he will exhale it all at once, doing 50,000 damage to each player. However, the damage is reduced by 25% for each stack of Inoculation you get, so if you got three stacks you only take about 12-13k damage.
The only time that you might be asked to move is to get the gas spores around. Each spore spawns on a person. The whole raid needs to be next to a spore when it explodes, which is 12 seconds after it spawns. If, by chance, all spores spawn in the melee group, then one of the players with a spore needs to run out to get to the ranged dps so they can get Inoculated. You’ll need to set that up with your raid in advance. Just make sure that you are near a spore when it goes off. If the spore is on you, make sure you are close enough to the tanks so that they get the Inoculation.
Other than that one possibility, you’ll be able to stay put and do big, big dps in this fight.
One other piece of advice – Festergut can do a targeted AoE effect that makes people vomit for 6 seconds. He only casts it on players at range, so we rogues don’t have to worry about this. However, if there are fewer than three players at range (eight in 25-man) he may cast it on melee, which would be bad. Make sure your raid has enough players at range, and that they are spread out so they don’t all end up puking.
The fight sounds simple, but that’s just for melee dps. The tanks will be switching to manage a stacking debuff (so be careful with your Tricks if you use it on the tank). Healers need to switch from raid healing to tank healing as Festergut inhales gas. None of that affects the rogues, though.
A note about a “just in case” situation… if somehow you don’t get all three stacks of Inoculation then I’ve read that you can avoid his 50k damage explosion by using Vanish just at the instant the cast goes off. I haven’t tried it myself, so take this advice with a grain of salt.
Festergut has a couple of attractive drops for rogues. On 10-man, he offers Precious’s Putrid Collar for your neck slot and Plague-Soaked Leather Leggings. There’s a slow mace, too, if you have seen any mace rogues out there.