Arcane Keysmith is not only one of the most powerful Mage cards in The Witchwood, but also one of the best-designed cards in Hearthstone.
The low cost and flexible effect make it a sure winner. This card will not only see play in Secret Mage decks, but in all other Mage decks as well ... except the odd-cost decks, of course.
Just imagine having a choice of setting up a secret that you need in a certain moment, even if you don't have it in your deck at all. Your opponents will have no choice but to surrender.