Here is the full list of all 47 ECHO achievements.
Finish the game on Ultra Hard
Pick up every orb in every caste level
Collect all Voices
Complete the fifth Verse
Collect 100 Voices
Have Echoes play the harp and piano at the same time.
Complete the third Verse
Complete the second Verse
Distract 5 Echoes at once with one Crystal Ball
Kill 3 Echoes by shooting a Sun
Throw 20 Crystal Balls
Eat 5 pieces of fruit during a single blackout
Eat 20 pieces of fruit
Shout and get the attention of 8 Echoes at once
Use Area Scan 20 times
Have Echoes know how to sprint, vault, use doors and walk in water at the same time
Traverse infinity for a while
Collect a Voice by having an Echo strike it
Complete the first Verse
Push 5 Echoes at once with the Riot Gun
Line up and shoot 6 Echoes with a single shot
Look at yourself in the mirror excessively
Finish the game on any difficulty
Take out a Hyper Echo
Shoot 200 Echoes
Make a 2 cell energy drop during a blackout
Reach Chapter VI
Complete the fourth Verse
Collect 50 Voices
Get Foster back
Push 50 Echoes
Get 4 additional Cell capacity slots
Reach Chapter V
Kill 10 Echoes with Crystal Balls
Take out 47 Echoes with the stealth takedown
Play the whole piano piece during a blackout
Collect 25 Voices
Tag 100 Echoes
Get 2 additional Cell capacity slot
Reach Chapter IV
Pick up 50 Suns
Collect 10 Voices
Push an Echo over a railing
Get an additional Cell capacity slot
Reach Chapter III
Line up and shoot 3 Echoes with a single shot
Activate the palace