Morkredd

In addition to the other solution, I've made a clip that shows where you can find the mural in the level "The Sewer". It was bugged for me, as you can see in the clip the mural didn't appear.



Note that there isn't a Chapter Select option when you finish the game, so if you miss the mural you have to replay the game.

Found this mural after you go across the 2 pipes then there is a cut scene of someone pulling the level opening up the floor( can’t miss it as it’s only one way through)

You have to spilt up over a small bridge at the end of the path...one pushing the ball and the other staying out of the shadows till you get back to the level. Once you’ve shut the floor bring the ball over to the other person and go back down the path the person without the light just came up and past the little bridge you crossed before you’ll see it on the wall