In a calmer state of mind, the nogitsune was have been fascinated by the boy made of ice. He would have retreated to a better place and time, sought what made the supernatural creature (for so he thought Bobby was) tick, and then found a way to manipulate his way into the boy's life. A being that could turn himself into ice and resist the elements was both knew and valuable. The nogitsune had been in this world long enough to understand he was probably looking at a "mutant" but he was not in the frame of mind to manipulate the creature while he (Bobby) was alive. Angry and haunted with old images long abandoned, the nogitsune simply wanted to destroy the creatures of this world that opposed him. He didn't want to play a game right now.
Up until the split second before Bobby formed the shard, the demon hadn't realized Bobby could manufacture projectiles. A moment before, the nogitsune had simply been facing an arrogant boy that didn't know better than to run. He wasn't expecting the shard of ice, and he didn't react quite in time to avoid it. Partly distracted by yuurei that only he could see, the piece of ice appeared in front of Stiles' face almost before the nogitsune realized Bobby moved. He hissed, a sound like a dying snake, and blurred. Black shadows gathered, and the nogitsune moved Stiles' body with unnatural speed--though not quite far enough. The shadrd missed his face and lodged into Stiles' shoulder, knocking him backward.
Already trailing blood, Stiles slid backward several feet into a collapsed desk. The oppressive atmosphere of gathering mist contracted like a piece of paper crumpling, then expanded again. "Chikou shou," the snake hissed again, rolling onto his side and quickly gaining his feet.