The meaning of Sea monster in dream | Dream interpretation
To dream about a sea monster suggests that issues from your unconscious are struggling to come to the surface. You may need to see yourself more clearly, and face the unpleasant aspects of yourself, in order to become the person you want to be.
If you killed the monster in your dream, you will successfully deal with your personal issues and rise above them.
Sea monsters are mythical in nature and were created by seafarers of old telling tall tales. Any creature that lives in the deep ocean is a product of the unconscious mind. In the case of a mythological creature that might fall in the category of sea monster, what is being expressed relates to overblown fears of your own creation.
Symbolic of a demonic entity or attack on your life, Ps. 74:13