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