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