Here is the full list of all 20 An Occasional Dream achievements.
Recruited Royce and set off on your quest.
Recruited Jarvis into your party.
Recruited Odette into your party.
Recruited Ferne into your party.
Killed Malandro.
Killed Vilikimas.
Defeated Oyunlar.
Killed Elokuva.
Defeated Impudenza.
Killed Umor.
Killed Haridus.
Gained access to the Metal Balloon.
Opened up to Odette in Buona.
Completed the game.
Entered the bonus dungeon.
Killed the first overworld boss.
Killed the second overworld boss.
Killed the third overworld boss.
Killed the fourth overworld boss.
Killed the final bonus dungeon boss.