Answer:
Large as a mountain, small as a pea, Endlessly swimming in a water-less sea.
Tool of thief, toy of queen. Always used to be unseen. Sign of joy, sign of sorrow. Giving all likeness borrowed.
I drive men mad for love of me. Easily beaten, never free.
Crooked as a rainbow, and slick as a plate, Ten thousand horses can't pull it straight.
They have not flesh, nor feathers, nor scales, nor bone. Yet they have fingers and thumbs of their own. What are they?
I appear in the morning. But am always there. You can never see me. Though I am everywhere. By night I am gone, though I sometimes never was. Nothing can defeat me. But I am easily gone.