Here is the full list of all 14 Class Kingdom achievements.
Destroy the first boss in the game!
Do 100+ damage to a single monster
Do 200+ damage to a single monster
Finish the 2nd world successfully
Finish the 4th world successfully
Choose a class for the first time
Find the code hidden inside the first world
Finish the first map
Gain more than 100 exp in a level
Choose Archer as your class
Choose Fighter as your first class
Choose Sorcerer as your first class
Destroy the first dragon
Enter the SECRET code in the first world