I love the idea, and would really enjoy building decks based around this card, but I have some concerns.
I don't like the fact that it doesn't take up the weapon: and that it duplicates it. This may be better if it can only be used on your weapon, and you then lose the weapon to the creature. Or perhaps multi use with a % chance to steal if used on an enemy, or a single use guaranteed steal when used on your own weapon.
As it stands its OP IMO.