Hello, I would like to offer two tips for the Forgemaster Throngus encounter in Grim Batol, which I hope will help PUGs out there... What I've found is that a few simple pointers really turn the group around.
1. Stacking on boss during shield phase
Don't do this. Half the time, rocks will start to fall on top of him and people will just sit there without realizing, and you will wipe. The strategy I've found that is PUG-friendly is to stay either stacked or spread out (either is fine) relatively close to him (15 yards or so), anywhere there are no rocks falling, and when the fire changes direction to you, simply strafe left or right. If rocks start falling above you, again just go left/right. This works because the breath is actually quite a narrow cone. The fire won't actually hit you much (the rocks are much more dangerous) and if you stack its even easier to aoe heal it. Melee/tank stay on boss and just sidestep fire. If rocks start to fall above boss, join the ranged. What I do is put a mark on myself and ask people to follow me.
2. Cast time debuff
I don't know when or how this happens, but you will get this debuff that has X stacks that greatly increases ur cast time, making casted heals useless, and generally the tank will die and you will wipe. What you must do as soon as you get this debuff, is keep casting instant casts (hots, dispells, anything that is instant) until all the stacks and the debuff fall off. Waste mana if you have to, or you will wipe. Every instant cast removes one stack of the debuff.
Good luck and have fun