Here is the full list of all 11 Dormant World achievements.
Listen to everything the stranger has to tell you.
Have 7 hearts.
Have a waterskin capacity of 7.
Defeat Icelus.
Defeat Phantasus.
Defeat Hypnos.
Defeat Morpheus.
Defeat Icelus on Hardcore mode.
Defeat Phantasus on Hardcore mode.
Defeat Hypnos on Hardcore mode.
Defeat Morpheus on Hardcore mode.