Answer:
I build up castles. I tear down mountains. I make some men blind. I help others to see.
What is pronounced like one letter, written with three letters. And belongs to all animals?
Tall in the morning, short at noon, gone at night. But I'll be back soon.
Only one color, but not one size. Stuck at the bottom, yet easily flies. Present in sun, but not in rain. Doing no harm, and feeling no pain.
I can be short and sometimes hot. When displayed, I rarely impress.
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?