Here is the full list of all 28 Starry Knight achievements.
Finish tutorial in any difficulty
Defeat the Reaper in normal difficulty
Defeat the Flying Fox in normal difficulty
Defeat the Thresher in normal difficulty
Defeat the Sculpture in normal difficulty
Defeat Discouragement in normal difficulty
Defeat Poverty in normal difficulty
Defeat Madness in normal difficulty
Defeat Despair in normal difficulty
Complete story in any difficulty
Complete game in normal difficulty
Complete game in hard difficulty
Defeat the Reaper in hard difficulty
Defeat the Flying Fox in hard difficulty
Defeat the Thresher in harddifficulty
Defeat the Sculpture in hard difficulty
Defeat Discouragement in hard difficulty
Defeat Poverty in hard difficulty
Defeat Madness in hard difficulty
Defeat Despair in hard difficulty
Kill all 5 crows
Die together with a boss
Kill a boss with Venus Drop
Kill a boss with Scream from Hell
Kill Reaper with Crow Attack
Steal in total 100% health in one boss fight
Defeat a boss without taking any damage
Defeat all bosses in hard difficulty with less then 50 damage taken from each fight (bleed damage from final boss is not counted)