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