Which witch?

Draco the Despicable has decided to take a wife! She must be a witch of the darkest powers - but who shall it be? To find the most fiendish one, he holds a spell-casting competition. Luna, the white witch, desperately wants to be a wicked enchantress - but all her attempts at blackness go horribly wrong. How is she to sink to the deepest depravity in only seven days?