There's three groups of Dragon Balls, each with a special power and evil. Some grant strong wishes, some grant weak all grant a different amount of wishes. The Earth dragon balls are the main ones which grant one wish thats strong and can bring a whole group of people back. The Namek dragon balls are the second ones they discover with Frieza and they grant 3 wishes but can only bring one person back at a time. Then the last ones which are spread throughtout the universe the Dark Star dragon balls. These dragon balls can explode the earth if not found within a year these reveal the z crews strongest and darkest enemy, Evil Shenlong.