Toon cloud

Mesh cloud

Render a cloud with a mesh, and use a shader to simulate the cloud's movement and shape change.

POM cloud

Use the Parallax Occlusion Mapping to sample noise texture.

Volume cloud

Use the Ray Marching(GDC) to sample multiple FBM noise(Perlin/Worley) texture.
TODO: FBM parameter still need to be adjusted, and the performance is not good.

Ref

Environment asset: Pure Nature (From unity asset store)
Water shader: Toon water