Flood -
Addition of water.
Render is a big work which requires a particular care concerning the lights and the reflections.
The final texture of water is a mix of several photographs of rivers, ponds, etc…
Some steps for the water texture
The mix between different layers is done by using the blending modes.
Characters - The light imports enormously for a coherent integration of the characters.
I still use «density» tools and blending modes to associate the different elements.