Here is the full list of all 24 Glimmer in Mirror achievements.
Investigate 10 points of interest.
Obtain your first Spirit.
Collect every Spirit.
Defeat Rat Owl, boss of the Forest of Origin.
Defeat Mimilin, boss of the Aromatic Plain.
Defeat Garfield, boss of the Prayer Tower.
Defeat Vorgl the Giant Dragon, boss of the Crystal Hill.
Defeat the late King Danudar, boss of the Onyx Castle.
Use the Owl Station for the first time.
Unlock every Owl Station.
Complete the storyline and awaken the Heart of Curiosity.
Complete the storyline and awaken the Heart of Kindness.
Complete the storyline and awaken the Heart of Bravery.
Complete the storyline and awaken the Heart of Resilience.
The girl repaired the world in the mirror.
The girl and her friends saw the true Glimmer.
Synthesize Glimmer Crystal for the first time.
Collect every Feather stone and Glimmer Crystal.
Collect 2000 Source Crystals in total via Figurines.
Obtain Feather stone for the first time.
Unlock every map in the Mirror World.
Knock back 50 monsters.
Defeat monster with the clever use of thorns.
Freeze objects 50 times with Gathering Light.