Shadowbane Cavalry

Stockpile {w} (Exile this card from your hand: It gains "{w}: Put a cache counter on this card." and "You may cast this card from exile if it has a cache counter on it with its cost reduced by {1} for each cache counter on it.")
When Shadowbane Cavalry enters the battlefield, exile target creature with converted mana cost 3 or less an opponent controls until Shadowbane Cavalry leaves the battlefield.