The cloud is masked indeed; by a soft ring (2 simple shapes merged) for the outer dust, with a height restriction and 0.5 coverage and 2 vortex shaders (Y and Z), and a circle (color at 3 for more intense cloud) for the inner, which are then warped by 2 warpers, small scales and a big scale for the grand movement.
The terrain is a perlin dotty mask raised by displacement shader, then a compute normal, then some masked (some vertically stretched) displacements in normal and lateral direction, including the available square noise setup, and a low octave strata shader (also masked by PF). Not even a compute terrain, by the way, which makes it render pretty fast. An hour or so for the biggest.
The colors are reds and greens merged normal, then hauled through a adjust saturation (blue node) with another fractal as 'mask'.
