Jack-O-moon was made to protect Lunar from Eclipse, BloodMoon and Stitchwraith. 
He also can be called Jack for short because his name is long. He can be creepy but is actually is friendly. 
He can glow in the dark like a jack-o-lantern and acts really stupid. He sometimes breaks Lunars favorite stuff because he thinks even the smallest details protects him. He knows that Sun, Moon and Earth are Lunars siblings and thats why he kinda trusts them. He was made by Solar aka Lunars friend.