a summary of dark world mechanics per chapter:
ch1 - inanimate objects can be darkners, and they are the most common type; darkners may not resemble their light world form
ch2 - intangible but real things can be darkners (ex. spamton=spam email; swatch=drawing program); creating a dark world requires a sharp object and tons of determination
ch3 - confirming that darkners represent something in the light world + concepts can be darkners (lanino and lanina = weather channel; shadowguys = shadow puppets)
ch4 - dead people can be darkners if there is a memento of them exist during the creation of the dark world; the dark worlds are a reflection of their creator
ch5 - inanimate living things can be imbued with sentience; in the creation of darkners, they can be influenced by other things/concepts (ex. yellow = cowboy shows, blue = butterfly, aqua = memory of kris, seth = memory of asriel)