Strategy

The Tank will pick up Festergut and keep him in the center of the room, melee attacks from behind as normal and ranged/healers spread out around half of the room more than 8 yards apart. Throughout the fight Festergut will cast Vile Gas on a random ranged player, causing them to then vomit on anyone within 8 yard which gives them Vile Gas also, so if players are spread out only 1 player at a time should get hit.

Once the boss is pulled the room will fill with Gaseous Blight which deals Shadow Damage every 2 seconds. About every 30 seconds Festergut will Inhale Blight, lessening the damage of Gaseous Blight but increasing his melee damage on the tank by 30%. He will cast Inhale Blight 3 times, giving him +90% damage. At the time when the 4th Inhale would come he instead cast Pungent Blight which deals ~50k Shadow Damage and returns Gaseous Blight to full and his melee damage to normal.

To survive the Pungent Blight, raiders must get stacks of Inoculated. Every 35 seconds 3 players will be targeted with Gas Spores.

Everyone must get within 8 yards of a player with a Gas Spore. If no one in melee is targeted one of the ranged must run in to apply the stack to them. If 2 players in melee get a spore one needs to run out to cover some ranged players. Good communication is needed to make sure everyone is in range of a spore. The Spores explode after 12 seconds applying 1 stack of Inoculated and deal ~2k Shadow Damage. Players must then be quick to spread back out to avoid multiple people getting hit by Vile Gas.

Throughout the encounter the tanks will be getting a stacking debuff called Gastric Bloat which increases their damage by 10%. However if the stack reaches 10, the tank will explode and deal 50k damage to the entire raid. Therefore tanks need to switch after 9 stacks. The debuff last for 100 seconds so the rotation will need to be very tight in order for tanks to not get a 10th stack.

This is a DPS check. Festergut has a 5 min enrage timer.