If you move right in the first cast. The second cast will copy your movements from before. If someone in the group runs across the map you will see a green swirly also run across the map the next time it casts the ability.
You can use it while it is targeting you, but before it goes off. Turtle will work. Shadowmeld works too, but I think it makes the boss target someone else lol.
There’s like a little half circle off to the right side.