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