Your current multiplier is shown underneath your health/stamina bar and you’ll need to kill enemies to build your multiplier up to 6 without taking a hit. Once you have x6 multiplier just block or continue killing enemies and avoid getting hit for another minute and the achievement will unlock.
This can be unlocked on episode 9 with a fully upgraded Lori. She has an ability to automatically dodge for you which can be a great help. Playing in co-op can help but the other person has to kill a minimum amount of enemies as you may clear the level without getting the achievement.
Develop Lori´s skills enough so you have poison and mind control. Hide in the shadows and then use mind control followed by poison. This can easily be obtained on the first level if you have maxed out both abilities. After using poison, hold to block incoming attacks. You access Lori´s special abilities by holding and then pressing the button assigned to the power you want to use. Repeat as needed. When you get the x6 multiplier, you can just stay in the room for 60 seconds if there are no enemies left alive. If you still have enemies around, hide in the shadows or just block with until the achievement pops.
Play as Lori on Issue 2 and play until the part where you're required to pull three levers in a specific order. Keep on pulling the lever on the very left over and over whilst sustaining your combo by hiding in the shadows and increasing your combo (pressing Y makes her throw disc-shaped objects that increase your combo). Keep repeating until you have a 6x combo. Once you have it, hide in the shadows for one full minute and the achievement should unlock. (Thanks to McGoogles)
Max out Vanish, Reflexes, and Venom Cloud for Lori. Once that is done, visit Issue 2 and just press and to kill the enemies. Try to avoid them as best you can. Move on to the next pages but wait for stamina to fill up beforehand. Once you have the 6x and the enemies are clear, feel free to just stand there. Thanks to Tyger7 for the stragey and the video below.
super easy. on the first level play as lori and max out razorspine. After you do that all you have to do is hold both triggers which blocks and hurts any enemy attacking you which builds your multiplier. when there is no one near you throw a few knives then hold triggers. When you hit x6 just keep blocking until it pops up. did it first play through in first level.