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