Even though it was not featured in the film, Coma the Doof Warrior (the flame throwing guitar guy) had a backstory that was created by George Miller: Immortan Joe found Coma in a cave with his mother’s head and took care of him. Coma made a mask out of his dead mother’s face to honor her whenever he went to war.
Even though the screenplay was written, the crew relied mostly on storyboards to shoot the film.
The silver spray the War Boys use while going to battle is not just a ritual. The spray keeps them high and devoted to Immortan Joe. Also the gesture made by them is the sign of the engine of V8.
The people walking on stilts in the green place are the boys left by the old ladies when they moved.