Here is the full list of all 21 Heroes of Eternal Quest achievements.
Defeat Riptar
Control 5 enemies at once
Poison 150 enemies with your attacks
Reach level 20
Use a torch to unfreeze 4 buildings at once
Defeat Skar
Unlock all the heroes
Complete all Citadel upgrades.
Discover the dark secret by destroying the tower's heart
Defeat 20 Sand Warriors
Complete the fourth floor of the tower
Conquer all floors of the Shattered Tower
Craft a One Ring
Defeat Zurik
Kill 50 dragons
Kill 50 Urfsark
Eliminate 60 enemies on the third floor with the ice element
Kill 250 spiders
Destroy 40 buildings throughout your adventure
Defeat 20 Rat Men
Defeat Rafne