Characters that is not purchasble with gold or with Blue Diamonds. Some of these characters may no longer be attainable at all if you do not already own them. These characters are obtainable by buying Diamonds (equivalent to riot points from LoL). The diamonds fill up VIP Points which are the ingame currency to buy these heroes, 500 vip points per hero. It is also possible to aquire these heroes through special events on the launch of new servers by getting 3-20 victories, sometimes by multiple first victories(the first win of the day in arena or bf mode).
Not to be confused with Blue Diamond Heroes, which are characters that ARE purchasable, but only through the use of the in game cash currency Blue Diamonds.