As stated above, the Night Flutter is simply an Air Screamer with it's head covered by a mass of worms, just as a Wormhead is the same with a Groaner. However, unlike the Wormhead, Night Flutters have some more obvious changes from their Fog World variant. Night Flutters are more humanoid than Air Screamers, and their skin is also darker.
The Night Flutter's worm head may symbolize Alessa Gillespie's disgust for creatures such as worms. The Night Flutter could also prove symbolic of Harry Mason's belief he may be losing grasp on his sanity. Worms are common decomposers, and seeing a mass of the creatures completing covering the creature's head could be a metaphor for one's sanity being eaten away.