Very slow ambient fog and smoke for overlay

Background, Clouds, White, Motion, Slow, Abstract, Composite, Mist, Cloud, Organic, Real, Strong, Atmosphere, Air, Effect, Black, Focus, Damage, Overlay, Transition, Climate, Fog, Frame, Explosion, Smoke, Gas, Floating, Channel, Cinematic, Alpha, Realistic, Left, Chemical, Steam, Blow, Vapor, Right, Haze, Thin, Obscure, Postproduction, Puff, Very, Desaturate, Disappear