The game won`t be on big sale anytime soon. We might have a mini sale next week - but it`ll only be like 3$ off. Every week or so we have various promotions though - different free unit - be it Dragon or Dwarves or a price drop. We usually announce it with our newsletter and on our website.
But to be honest - the current promo with a free Haunter Dragon is a pretty sweet deal as is. It`ll only be here for 2 more days