The creature's wiles served it in good stead. The rock would indeed intersect the shadows that Cruallassar is preparing to form from. However, in this case the nature of the Ranger's power would work against it. He could not reform within another object...either the object would be displaced, or Cruallassar would be, in the instant before he materializes. Not only this, but the power was very difficult to keep precise. Cruallassar had mastered it to a point where he could be precise within millimeters, however he rarely did on a normal basis, since his physical abilities were nearly always enough to keep the effect the same however he appeared, and precision to that degree was almost never needed. Thus, he would usually be content to appearing within a few inches of where he needed to be. And his reflexes were easily enough to react at least in part to the blur of motion of the rock flying at him, thus to affect in part how he materialized. This lead to the Ranger appearing a few centimeters in to the space the rock had just vacated, loosing his arrows unhindered.

This is not to say his plan was not partially disrupted. The fact that the beast had the cunning to hurl a stone at where he was appearing before he did showed a level of planning and analysis he had not been planning on...one that in hindsight had not been the first sign, his having caught and thrown his grenades showing similar signs. The thing had managed to predict his moves with great accuracy for a monster. However, not even that prediction would save him from the arrows he still lets fly, before twisting into ethereal shadows again to observe the effect of his efforts from a safe environment.

The first net's presence...or lack thereof...is entirely unnoticed, due to his visual limitations.