Answer:
Something wholly unreal, yet seems real to I. Think my friend, tell me where does it lie?
What is that over the head and under the hat?
What kinds of men are always above board?
Look into my face and I'm everybody. Scratch my back and I'm nobody.
At first, I am nothing. Add something to negate. Add again to oppose. Add again to find the time to draw. Add once more to find nobody at all.
You use it between your head and your toes, the more it works the thinner it grows.
Difficult
Animal
Easy
Food
Funny
Kids
Logic
What am I?