Kara, Spellbinding Witch

{1}{b}, Reveal Kara from your hand, Spellbind 1(Increase or decrease the original converted mana cost of a permanent you control by 1.) You may play an additional {b} when revealing Kara, if you do, instead target one permanent you do not control, Spellbind 1.
When Kara, Spellbinding witch enters the battlefield, choose a converted mana cost then destroy all nonland permanents with that converted mana cost.