As with many of these raid/boss guides there's only so much that is specific to any class. The Plagueworks doesn't include any bosses that get us locks doing anything fancy or new. That said though they are great fights and interesting in their own right. This guide is aimed at warlocks but probably of use to all casters. No doubt the comments will be full of neat little tricks that I have missed but as I breached 2000 words I had better stop where I am and not start explaining how to one-shot things with Eye of Kilrogg and Dark Pact.
Festergut is the simplest of the Plagueworks bosses but that doesn't make him easy. He's essentially a gear-check, though obviously you need to know how to apply that gear as well. The tanks get checked to see how hard they can be battered for thirty seconds at a time, the healers checked on how well they can swap from healing everyone a bit to healing one person a huge amount. Then there's the DPS, we may not be the drums of the raid group but you never tanked or healed a boss to death, we need to end the fight before those support roles fail.