Here is the full list of all 21 Groove Gunner achievements.
Complete training.
Complete your first song.
Start Groove Gunner for the second time.
Get 20 perfect score shots in a row.
Collect a record from 5 different songs.
Collect 3 Legendary records.
Shoot 1000 targets.
Block 2000 bullets.
Complete 40 songs.
Complete a song on executioner with "Color Override" set to on and all RGB color sliders set to 100.
Complete at least one difficulty for all of the songs in the game that were included at the initial release.
Block 40 consecutive bullets.
Fail a song for the first time.
Get 50 shots in a row.
Complete a song in 4 difficulties
Complete a song on Recruit while hitting all Targets and blocking all Bullets
Complete a song on Marksman while hitting all Targets and blocking all Bullets
Complete a song on Sharp Shooter while hitting all Targets and blocking all Bullets
Complete a song on Executioner while hitting all Targets and blocking all Bullets
Complete a song with a perfect score
Play a custom song