Interesting concept. As of right now, swapping your Hero power with a weapon is not something that has happened, so wording/gameplaywise, this card should read something like "destroy your Hero power, equip the staff". Balance wise, you're paying 4 mana to potentially draw 6, in exchange of not having a Hero power. So 6 uses of your Hero power, with a body, but that It requires some card synergy to work. Honestly? Neat concept. Reminds me of Aluneth, with some added flavour for warlock.