Once Upon A Time Riddle

So you think, that your clever and smart,
and you're a master of art?
Well, if that's the case,
it should be easy for you one after another to erase.

But I'm not so vile,
I'll give you even a hint or two,
with a tiny smile.
So it's up to you.

I know many people in the Enchanted Forest,
I helped them from time to time,
even if they have no money and no crest.
Often the get from me a new chance for a crime.

A little advice from me to everyone
doesn't matter if you're a daughter or a son.
But you should never break an deal with me,
or I will be your worsest enemy.

Breaking a deal, would be more than a gravely mistake,
I'll cling to you like a vivid rattlesnake.
You're never will be getting a rest,
if I found you, it'll be your final test.

Maybe youre lucky, and I only demand your hand,
otherwise it could be your last stand.
So I made my point clear,
and as long as you behave, you have no reason to fear.