Draco did look up, and immediately cast a sharp Stupefy, which hit the creature and appeared to slither its way down the flanks as if the spell was moving on an oily slick surface, and didn't appear to have any lasting effect at all. His Petrificus Totalus slowed it down, it was visibly slower, but even as Draco watched, it seemed to shrug off the effects of a spell meant to paralyze it completely.

Hell, what was it? He'd thought an animagus, perhaps a partial transformation, but an animagus would be affected by Stupefy, they were as vulnerable to that whole class of spells as any other wizard, and all of this went through his head as he backed hurriedly away from it, knocking over a wooden-backed chair in his haste, casting about for spells he could use that could affect something like this.

"Protego," he snapped, holding out his wand and putting a Shield charm between himself and the, well, the monster, which was apparently real after all, it might give him time to think.