the movie was really scary/scaring
я знаю, что ответ - scary, мне он неважен
мне необходимо адекватное ОБЪЯСНЕНИЕ, почему здесь scary, а не scaring
не игнорьте, пожалуйста(

SCARING:

progressive tense requires form of be:

is scaring +direct object (am/are/was/were)

The moving curtains are scaring me.

Gerund is using the word as an activity (noun)

Scaring children is not nice. (the action of scaring children)

SCARY is an adjective:

Scary children are not nice. (children who scare)

This movie is scary.