An exploration of volumes and vector fields manipulation in Vex, combined with smoke solvers. Using vex allows modeling of complex elements while maintaining control on the art direction, better than using simulation only.
I created a manual smoke sim for the growth of the cloud, then exported its velocity field to advect the skull volume using Vex. I then mixed the densities of both the cloud and the skull VDBs to create the effect of a skull appearing in the cloud. The only animated parameter is the volume mix.