Here is the full list of all 20 One Many Nobody achievements.
Complete the tutorial levels
Complete the factory area
Complete all levels in the factory area
Complete the laboratories area
Complete all levels in the laboratories area
Complete the headquarters area
Complete all levels in the headquarters area
Destroy the factory and save the clones
Save the factory and sacrifice the clones for a greater good
Clone yourself 100 times
Clone yourself 300 times
Clone yourself 500 times
Kill or sacrifice 100 clones
Kill or sacrifice 300 clones
Kill or sacrifice 500 clones
Kill a guard
Kill a spiderbot
Defeat The One
Read all the Dr Symfel diaries
Kill another clone using a timed one