It will bring about a frightening change in mood and behavior.
mysterious, frightening, scary....
That movie was frightening .
more frightening
Yes, the word 'nightmare' is a noun, a word for a frightening dream; a frightening or horrible experience; a word for a thing.
The prospect of spending the night in the haunted house was absolutely frightening. Walking in the woods can be frightening if you are alone.
frightening
Frightening
Vampire is a seven letter word that describes a frightening Halloween creature.
I think you are asking what the word 'atmosphere' means when used in connnection with a story, play or film. Its just another word for the mood of the story. The mood can be pleasant, amusing, frightening, cruel, despairing or whatever depending on what type of story it is and what emotions the author is trying to arouse in you.
very scary
If you mean the word "mood" then it has only one syllable.