I see two problems with that. 1. Magister sphinx costs 4WUB plus 4WW for open the vaults puts this combo at 13 mana to pull off and the second problem is that Magister Sphinx isnt in your deck. The plainswalker Sorin Markov might be something to think about
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Hopefully ill eventually be able to afford -4counterspell +4 force of will
Flying defense?