Just unlocked this in the area after the 3rd boss, you will come across a battle flag right next to a lightning wyvern spawn.
One of it's attacks is 3 bolts of lightning which travel towards you, if you throw the poison bubbles (first spell in the metal skill tree) on the floor as he uses this attack it will cancel out the lightning bolt that hits it and unlock the achievement.
I got this along with someone else doing this exact thing so definitely works and pretty easy to do with a flag right next to it.
Just extra info if you're struggling to find the area, before the 4th boss from the closest flag go up the scaffolding, past the big hammer guy and you will find a big door which can be opened from this side only, open that and the area is directly in front of you