What is the Development of Beastie up to chapter four

The beastie is the culmination of all the boys' hidden fears..... the beastie is their fears. Fears of the unknown, shadows, the woods, the noises..... each of these things is a part of what becomes the "beastie", Each boy's fear ends up added onto the fear of another, and child by child, it grows to such an extent that one of the boys ends up dead (Simon).