Answer:
Of no use to one, Bliss to two. Men lie for it. The baby’s right,
I build up castles. I tear down mountains. I make some men blind. I help others to see.
What is it that given one, you’ll have either two or none?
A man shot two arrows at its center and missed both times, but using a sword swung once at its center and hit it twice.
Long and think, red within, with a nail at the end.
People take me on walks and I run and have fun. What am I?