Originally Posted by The Narrator

As you move through the gray haze and on to the Hogwarts grounds, the first thing your well trained herbologist eyes may notice is that the flora here does not seem to be particularly out of sorts. Nothing that wouldn't be expected of plants that had not seen the sun for a prolonged period of time. Your samples here, should you be able to collect any, would reveal just as much.

No toxins. Nothing foul at play. Nothing to fault in the quality of the air. Simply flora starved for sunlight.

......you will also discover that your Bubble Head Charms are worthless against the true nature of the mist....

........which seemed to thicken as you step closer and closer to the castle itself (holding on to a rope to help guide you back a stroke of genius)...

It happens suddenly. Indistinguishable shapes reach out from the murky clouds and grab hold of your legs. Latching on tightly, they yanked hard. A shoe is torn off and discarded, but the shapes came back for more to yank on the leg proper this time with a determination pull you away from the group and into its depths....