Tap on the screen to select a hero or tower. Slide your selected hero or tower to an available slot on the battlefield. Fuse two identical heroes or towers to enhance them into a more powerful version. Position your upgraded heroes or towers carefully to defend your base against incoming enemies. Monitor the enemy's path and modify your defenses accordingly. Employ special abilities or powers by tapping on the hero or tower when the ability meter is full. Survive all waves of enemies to win the level. Think ahead your merges and placements to increase your defense's effectiveness.