This is a very specific instance, but my favorite was in Black Cove against that first abomination you come across (the water one that summons crabs). To reach it, you had to cover the vents for poison, so you could cross safely. I kept all but my archer back behind the clouds location, and initiated combat with said archer. After pulling my archer back to the line with the rest of my party, I set the abomination on fire with my caster. When it got close enough, I pulled the barrel off the vent cover, and released the poison gas. It set off a chain reaction that just continually whittled down the HP of the abomination, until it was dead. Simplest kill I ever had in the game so far.
That said, if the location of the fight has one of those vents, it makes for a great trap, since it continuously regenerates the poison cloud.
