Here is the full list of all 15 Nil-Ninjahtic: Ronin achievements.
Beat level 1
Beat level 1 with less than 10 deaths
Beat level1 without dying
Beat level 2
Beat level 2 with less than 10 deaths
Beat level 2 without dying
Beat level 3
Beat level 3 with less than 10 deaths
Beat level 3 without dying
Beat level 4
Beat level 4 with less than 10 deaths
Beat level 4 without dying
Beat level 5
Beat level 5 with less than 10 deaths
Beat level 5 without dying