Here is the full list of all 42 Monster Castle achievements.
Recruit a comrade 3
The Cave of Greed 1
The Sky City 1
Impregnable Defence 2
Questing Adventurer 2
Better and better 2
Attack Master 2
Gold Rusher 2
Decorated Warrior 2
Wino 2
Store gold 2
Recruit a comrade 2
Invincible Havoc-Wreaker 2
Decorated Warrior 1
Attack Master 1
Better and better 1
Wino 1
Gold Rusher 1
Invincible Havoc-Wreaker 1
Impregnable Defence 1
NEW_ACHIEVEMENT_DESC_1_27
Recruit a comrade 1
Store gold 1
Store gold 3
Better and better 3
Impregnable Defence 3
Attack Master 3
Decorated Warrior 3
Invincible Havoc-Wreaker 3
Gold Rusher 3
Wino 3
Questing Adventurer 3
Kingslayer 1
Kingslayer 2
Kingslayer 3
Domination 1
Domination 2
Domination 3
The Sky City 2
The Sky City 3
The Cave of Greed 2
The Cave of Greed 3