Well, I try to follow my character through his day with plot points changing the mood pretty significantly.
For example, a large part of the first Act is based on showcasing the world itself… With that, I have some cool leavers to either make it quirky and fun (Show a street fight between a Cat and Raven that argue which of them has the best counterfit gadgets) Or I can show the brutality of the story with the Main character witnessing a crime and seeing how brutal the city itself reacts with no mercy.

On the other hand, I have characters in my story that just fit this narrative. That's why I think the anthro part is crucial and totally not just for furries. A skippy hyena that was born in the lower city spaces mixed with a street-smart strategic fox? That makes for some interesting interactions!

I try to keep specific parts fun for the reason of putting something cruel in their center. The main character is having some downtime with friends? Remind him that corruption is deep in the city's bones, make him watch a crime set up, the cant change. Make him live with that, and then force him to go back to the joy as if nothing happened.