Riddle me this batman.............

You can find us in darkness but never in light. We are present in daytime but absent at night. In the deepest of shadows, We hide in plain sight. What am I?

Forward and forward I go, never looking back. My limit no one knows, more of me do they lack. Like a river I do flow, and an eagle I fly. Now can you guess, what am I?

What falls but never breaks, breaks but never falls?

When I am filled I can point the way. When I am empty, nothing moves me. I have two skins - One without and one within. What am I?

My life can be measured in hours, I serve by being devoured. Thin, I am quick, Fat, I am slow, Wind is my foe. What am I?

Walk on the living, they don't even mumble. Walk on the dead, they mutter and grumble. What are they?

What regularly changes shape, yet remains a sphere, is always there, but often not seen?