The story of 999 goes like this

I was once playing minecraft. I had made a new world. I went out to get some wood. As I was walking i hered footsteps behide me. I looked back and saw nothing... I felt fear. I don't know why i just did... I started walking back to my house wen I saw it.. I player like mob with the words "999" above its head. It was 100% blue and very wired looking.