Wanted: one wizard with experience repelling invading armies by drawing shapes in the air. Must provide own wizard robe and be okay with light in-app purchases. If this sounds like you, there's a game you should play called Magic Touch: Wizard for Hire.
The goal in Magic Touch is to keep enemies from landing on your castle for as along as possible by popping their balloons. Why they use balloons for transportation I cannot say. However, each balloon has a symbol inscribed on it. Draw that symbol in the air, and the balloon pops. You'll have to be fast to keep up with the onslaught.
Each game nets you coins that can be used to unlock new spells, helping you stave off defeat a little longer. There are a few small in-app purchases that grant you more coins, but they're tucked away in the menu and not pushed on you at all. The main IAP is a roughly $3 charge to get rid of the ads. If you want to give it a shot, get your references in order and apply by downloading the game.