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