Once you've beaten the game for either the good or bad ending on standard difficulty, Chaos difficulty will become available. It's effectively New Game+. Play through to the finish and get the good ending by making sure all five Smockula body parts are equipped.
Bear in mind that you need Relic level 3 skill to have all five equipped if you're playing solo. If you already picked up the body parts on the first playthrough, you won't need to do it again on the harder difficulty level.
Then get ready to do it all again for:
At the time of writing, both this achievement and the total anarchy equivalent are bugged and will pop regardless. Thanks for the tip BlackMage Felix.