Stars are earned through completing the Campaign Missions. You need to earn Stars to gain coins and to help you progress to the new areas in the game. Each level has 5 Stars available:
- Complete the level without losing a life = 3 Stars
- Complete a level with 15 lives left = 2 Stars
- Complete a level = 1 Star
- Complete Veteran Difficulty = 1 Star
- Complete Spec Ops difficulty = 1 Star
The first time you gain a new star will earn you 600 coins that you can use to unlock tower upgrades.