Every unit has similar Evolution unit materials needed depending on their rarity. However there are certain units that require special evolution materials such as Fei and Fang, Elaina and other Event units.
For Fei and Fang, the unit needs a special evolution material that only this specific unit needs to evolve.
For Elaina, she uses a different special evolution material.
The Brave Frontier Wiki has extensive information on Unit Evolution. Simply go to the Unit Evolution List on the wiki and search for the unit you wish to evolve to see what materials are needed.