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