Here is the full list of all 16 8-Bit Commando achievements.
Complete at least one versus match
Complete any mission in coop
Collect every type of powerup
Complete every mission on hard difficulty
Take out 81 bad guys
Complete the seventh mission
Complete the sixth mission
Complete the fifth mission
Complete the fourth mission
Complete a mission without dying or losing any health
Complete the third mission
Fire over 666 bullets
Complete the second mission
Complete any mission in under 2 minutes
Complete the first mission