Fear changes the bile, and that’s what the Man in Yellow feeds on
The finale made me think the Man in Yellow is purposely increasing fear and stress in the town because it changes the bile.
He says his favorite part is when they tear each other apart: betrayals, panic, deaths, hopelessness, because all of that would massively increase fear and stress. Stress can make bile more concentrated, and bile has historically been connected to fear/emotional imbalance.
Then we literally see him eating the liver, the organ connected to bile.
So maybe he isn’t just feeding on people, he’s feeding on bile that has been “filled” with fear and stress first.
It could also explain why the monsters constantly psychologically torture people instead of killing them quickly. And when they dissected the monster, the only thing inside was bile, which might mean that fear/bile is actually what fuels them.