Good question @TuralMammadzada! The general guideline is PG13.
On our common rejection reasons page it says:
Your submission does not meet our maturity content guidelines
Unfortunately, your file contains inappropriate language and/or explicit sexual, violent or drug-related content, which will need to be removed from all previews and download files. Please remove offensive material from future uploads before submitting them.
Take a look at what’s already in the library to get a feel for the threshold. Maybe this VideoHive thread on horror and Halloween content may also be useful.
Oh, and there’s always this to consider… 