I only learned about Shadow People about a year ago, and when I did I remembered an incident as a child. At about age 9 I was laying in bed wide awake one dark night. I saw one standing in my bedroom doorway. I thought it was my father and I said, "Dad?" And then it walked away.
It was a fully formed person, the shape of an average-height man. But it had no form or specific features, only a fuzzy black.
I am told that Shadow People are spirits that are trapped between dimensions.
More recently I learned that animals can be Shadow People too. About a year ago my companion and I were on a night hike, and wearing our head lamps. I saw what looked like a shadow bobcat pass in front of me. It was black and had the shape of an animal, but it was perfectly silent and fuzzy. I never told my hiking partner because I didn't want her to think I was crazy.
Maybe it was just a shadow created from my light, but it sure seemed real to me.