This video takes you through the scene file used to create the effect of dry ice flowing down over some letters. It uses the advanced characteristics of the apply_source node to create bespoke sources and sinks for the gas, and uses the gas dissipate microsolver to make the gas evaporate as it warms up. The scene file is at is worth watching the Sourcing and Smoke series of videos and, if you are starting from scratch, the Volumes series before this video.