Upgrade heroes

Each hero needs to raise stars to become stronger. When a hero is upgraded, the internal stats and skill stats (Skill) will increase. The upgrading mechanism is explained as follows:

• From 1 star to 2 stars: combine three heroes of the same kind or use your hero and an 'Upgrade Gem' to upgrade the hero

• From 2 stars to 3 stars: combine three 2-star heroes of the same kind