Answer:
I am a tale in childrens' minds. Though an illusion, I occur every night. I give them a fantasy, I give them a fright. What am I?
What has a bottom at the top?
I need to be taken from you before you can have me.
What is easy to spot but hard to find?
Face with a tree skin like the sea. A great beast I am. Yet vermin frightens me.
Whoever made me don't want me. Whoever bought me don't need me. Whoever use me don't know me.