Answer:
By Moon or by Sun, I shall be found. Yet I am undone, if there's no light around.
I make you weak at the worst of all times. I keep you safe, I keep you fine. I make your hands sweat. And your heart grow cold. I visit the weak, but seldom the bold.
I look at you, you look at me, I raise my right, you raise your left.
What word looks the same upside down and backwards?
We are five little objects of an everyday sort. You will find us all in a tennis court.
Walk on the living, they don't even mumble. Walk on the dead, they mutter and grumble.