Here is the full list of all 45 Soundfall achievements.
Complete 10 missions with 2 or more players
Complete all missions on Lethal Intensity
Complete all missions on Extreme Intensity or higher
Complete all missions on Dangerous Intensity or higher
Defeat 5 Discordians with a single on-beat Audio Bow attack
Defeat 10 Discordians simultaneously with Jaxon's Stage Dive
Complete 5 missions on Lethal Intensity
Reach Level 50
Gear up a hero with Legendary items in all equipment slots
Complete 20 missions in each environment
Complete 25 missions with each hero
Hit 10 Discordians simultaneously with Brite's Area Shield shockwave
Complete 5 missions on Extreme Intensity or higher
Complete 10 songs using the Free Play menu
Defeated Discord and saved Symphonia
Complete all missions in the Peaks
Complete all missions in the Jungle
Complete all missions in the Crypts
Complete all missions in the Desert
Complete all missions in the Depths
Open 100 treasure chests
Faced Banshee at Harmonia
Complete all missions in the Cityscape
Heal 2000 health using Minuet lifesteal
Hit 5 Discordians simultaneously with Ky's Scythe Toss
Complete the team wth Ky
Complete all missions in the Volcano
Defeat 25 Discordians with Nocturne detonation
Bring Brite on to the team
Complete all missions in the Forest
Deal 1000 damage-over-time with Bolero burn
Grow the team with Lydia
Complete all missions in the Beach
Hit Discordians 100 times with Requiem chain lightning
Recruit Jaxon for the team
Complete all missions in the Skylands
Defeat 100 Discordians with on-beat Audio Blade attacks
Break down an equipment item into gold
Fully slow 25 Discordians with Serenade freeze
Use gold to buy an item from the in-game store
Obtained the Audio Blade
Defeat 50 Discordians with on-beat attacks
Landed in Symphonia and completed the Tutorial
Complete all missions with a Platinum ranking on Lethal Intensity
Defeat 100,000 Discordians