After Rufus splits into 3 parts, one of the clones will fall into complete darkness and needs to light a fire. The problem is that Goal keeps crying when Rufus makes a sound interacting with stuff.
First things first DO NOT HIT SPACE. This shows all the places you can interact in the darkness. To get the achievement you have to do this without using the "show interactable" button.
You also need the pacifier from Baby Bozo which can be obtained through the other Rufus' to calm Goal down when you interact with stuff.
You can see if there is something to interact with because the cursor icon will change to a hand. Use this to "feel" your way through the darkness, the items are not too far away from both Goal and Rufus' eyes.
This is much easier on the console versions...