Jack of the mine

I was once playing minecraft on a world I had had for 3 mouths. I was mining in my mine. Everthing was fine. till it started to get wired. I dug into a room with 3 torches and 3 signs. The first sgin said " come and find ore" the next said " but" and the last said " look out for jack of the mine". There was a hole at the end of the room. I went to it. It led me to another room. A player like mob was there with the words "jack of the mine". The player like mob was wired and scary to look at. The top of his body was red the bottom was brown. I then was scared I didn't no why. I ran. man i ran. I came right to the door of the mine then I was killed from behide.