Some of those creatures were friendly, mischievous, others rather dangerous. Some possess animal features such as Kappa which is similar to a turtle. Other times they can appear as human.
There are also yokai based on household items. In the past the Japanese believed that every inanimate object had its own spirit and would cause bad things to happen to anyone who didn't take good care of it.Stories about yokai sometimes served as a warning to people to be more respectful to the things they use.
Japanese people have always had a certain fear of nature, but they have also felt an affinity with it. Scary but at the same time oddly likable, yokai perhaps embody the Japanese way of seeing the world.Even today yokai are living in our lives. "GeGeGe no Kitaro" is a famous manga series created by Mizuki Shigeru. It is about the yokai world. My favorite character is "Nezumi-Otoko".