I Am Round I Am Sharp I Am Small I Am Big I Exist Then I Don't
Riddle: I am round, I am sharp, I am small, I am big, I exist, then I don't. What am I?
Answer: The Moon. It's round when it's full, it's sharp when it's a crescent, its size can vary depending upon its phase, and it's gone when it's a new moon.
Source: https://riddles.com/index.php/2312
