Answer:
I grow up while growing down
A single syllable do I claim black was my most famous name; Fetal to mortals here below thousands have I slain in a single blow.
I like to twirl my body but keep my head up high. After I go in everything becomes tight
I'm blue, but when you see me I'm red. You don't see me too often. I'm there for you if you're hurt, but I'm good for you. What am I?
I'm not alive and yet I grow. Just put me next to where it glows. A favorite in summertime best with friends when combined
I am your mother's brother's only brother in law. Who am I?