In the case of this riddle, you should also clarify what do you think the riddle parts refer to...
...for others: by this, I am not saying that
Gil-Galad is right, you can keep trying...
...actually, let's make this clear:
Gil-Galad is
not right

I expected the Nazgul to be among the first guesses, but it's not right. But furthermore, please, try to be more specific of what do you think the riddle refers to (e.g. "I am dark as night = Nazgul is really dark"). Then I could easily explain to you why you are wrong