If the tip of his arrow shimmers, he is preparing an Impaler Arrow. Avoid being pinned to the wall at all costs; his Planted will do 2400 damage before you can even move again, and likely another 2400 to follow, killing anyone.
Don't forget that Resilience is a thing. If you find yourself at the end of an Impaler Arrow, try buying Resilience and watch the stun duration become non-existent.