Here is the full list of all 20 Atomik: RunGunJumpGun achievements.
Shoot the saw through the two large chambers and live to tell about it in 'Football Racetrack'
No saws dislodged in 'Stomach II'
No enemy ships harmed in 'Gridiron'
No enemy ships destroyed in 'Target Locked'
No mercy for turrets in 'Pew Pew Pew'
Collect All Atomiks in World 3
Collect All Atomiks in World 2
Complete a World 3 Marathon Run
Beat Omegaton
Collect all Atomiks
Beat every level in World 3
Collect all Atomiks in World 1
Beat a level without using the fly button.
Complete a World 2 Marathon Run
Beat Omegastroid
Die 100 times on one level
Beat every level in World 2
Complete a World 1 Marathon Run
Beat Omegalith
Beat every level in World 1