Here is the full list of all 15 Ravva and the Cyclops Curse achievements.
Finish the game
Clear all the Dungeon stages
Break the High-Score and finish the stage
Clear all the Desert stages
Clear all the Forest stages
Find 5 Hidden Power-ups in one playthrough without closing the game or returning to the title screen
Stack 5 extra lifes
Get your first Rainbow Star
Complete the Tutorial
Finish the game with an unexpected ending
Get 10 Rainbow Stars in one playthrough without closing the game or returning to the title screen
Score 500.000 points and finish the stage
Collect 5 lives during a single run in Master Mode
Defeat the first boss in the Master Mode
Defeat the final boss in the Master Mode