Although not useful in battle, specials are one of the most important monsters in the game. . They are the key to evolutions.
There are 5 regular specials, one for each element. An evolution requires specials of the same element of the monster being evolved in nearly every scenario(with the exception of evolving Lengendary or Mythic monsters).
Candy specials are required for some evolutions for supers, ultras, and epics. The type of candy is of the corresponding rarity. These can be found in Hall Dungeons, Raid Halls, Troop Raids, Prize Grabs and events.
Crystal specials are required for second evolutions.See Evolution for more information
Type of Rarity Specials
What you need to max level a special with another same element special using a feeding booster: