Here is the full list of all 25 Audio Arena achievements.
Kill 15 dots using missiles
Get 150 points using the bomb
Get 5 perfect beat syncs in a row
Complete a song
Get a combo of 100 dots
Kill 1 dot worth 15 points
Last longer than a minute
Get maximum sync bonus
Complete the song without ever going out of sync.
Complete a level without killing a dot
Complete a song with maximum beat sync
Kill 400 dots in 1 song
Complete a song using only 10 powerups
Complete a song with zero dots left alive
Kill 1 dot worth 100 points
Kill 1 dot worth 50 points
Get 400 points using 1 Bullet
Keep a mine alive for 15 seconds
Kill 50 Red Dots in a row
Get a combo of 250 dots
Get a combo of 500 dots
Kill 15 dots using an aimed missile
Kill 10 dots using a shield
Finish a song killing only purple enemies
Use a shield to kill a dot worth 50 points or more