Here is the full list of all 29 Kingslayer: The First Assassin achievements.
Kill the King
Complete the Level 28
Complete the Level 27
Complete the Level 26
Complete the Level 25
Complete the Level 24
Complete the Level 23
Complete the Level 22
Complete the Level 21
Complete the Level 20
Complete the Level 19
Complete the Level 18
Complete the Level 17
Complete the Level 15
Complete the Level 14
Complete the Level 13
Complete the Level 12
Complete the Level 11
Complete the Level 10
Complete the Level 9
Complete the Level 8
Complete the Level 7
Complete the Level 6
Complete the Level 5
Complete the Level 4
Complete the Level 3
Complete the Level 2
Complete the Level 1