Personally I'm very boring. I design Horrors according to legend and fiction. For me they are Astral creatures and as such they are "known". Horrors who are entirely new or unable to be put into words are the marks of the Insatiable. Still that makes for a diverse bunch as I don't make a difference between the genres of fictions. Want the Slender Man for your Eshmaki Predator? You can. Want the Other Mother for your Inguma Collector? You can.

Design is rather easy, I generally go from the Hunger, find a monster that corresponds and then interpret it in light of the Family....