The Scribbler takes simple vector based input (in the case of the online toy, your drawing) and creates its own drawing on top of it based on a number of simple rules. When a new scribble line is created it chooses a few numbers at random that eventually determine what sort of line it will draw. As it begins to draw it fine tunes those values to the type of drawing that you’ve made. Certain scribbles are better at following straight paths, others are better at outlining curves, and others are better for filling in large areas of color. Because there is randomness built into the program, each scribble is unique.
In the version I’ve posted on-line you can adjust some of the values that Scribbler would normally choose at random, such as line thickness, line color, and the dubiously labelled scribbliness setting, which in this case determines the maximum length of a scribble line. You are essentially collaborating with the Scribbler on a drawing.