Answer:
I can be simple or I can be complex. I can be found in this riddle or in everyday life. I can be shapes or even colors.
Cold head and feet; round as a ball; always turning around myself.
I am free the first time and the second time, but the third time is going to cost you money. What am I?
I am the kind of food monkey likes and people slip on me and fall in cartoons.
I am a king who's good at measuring stuff.
Whoever made me don't want me. Whoever bought me don't need me. Whoever use me don't know me.