Answer:
By Moon or by Sun, I shall be found. Yet I am undone, if there's no light around
Always wax, yet always wane: I melt, succumbed to the flame. Lighting darkness, with fate unblest, I soon devolve to shapeless mess.
I can travel from there to here by disappearing, and here to there by reappearing.
Runs smoother than any rhyme, loves to fall but cannot climb!
Whoever makes it, tells it not. Whoever takes it, knows it not. Whoever knows it, wants it not. What is it?
Iām grown from darkness but shine with a pale light. Very round I am and always a lady's delight.