Imaginary friends are pretty prominent in most cultures around the world. They're usually more prominent in regards to children, but there have been some adults who reported having imaginary friends. In Spidersilk the novel, Mark actually refers to Garrick as his imaginary friend. It seems that the two managed to befriend one another even though they were from different dimensions. This is actually a common theory around the imaginary friend concept. This definitely adds a very cool element to Spidersilk!