The Sentinel Tower can be used in missions to deal devastating damage to groups of enemy units.

Tap and drag from the Sentinel Tower to your target location, then release when you are happy with your target. While targeting using the Sentinel Tower you should see a line being drawn from the Tower to your finger along with a targeting marker under your finger.

The Sentinel Tower will slowly recharge out of battle, with each charge taking a longer period of time to do so. To speed up this process you can fully recharge the tower by using Gems in battle and from the Towers menu screen. In addition, you can send and receive free charges with your friends on Facebook from the Mailbox on the mission screen!