it says as it floats just inches away from the terrified Cecil's face with a grin.

This is a concept of when Cecil and Xander meet Cecil found a lock book that only he was able to open then the black mist gushes out and floods the library Cecil runs from it when he noticed that it was sentient and began the float towards him he tried to hide behind a bookcase but was cornered by it so we get this scene.

I should also note that Xander is not evil mischievous yes but not evil.