Final answer:
A visual effects artist in post-production can create a massive explosion using computer-generated imagery (CGI) and create a Chroma key shot by replacing the background with any other image or video.
Step-by-step explanation:
A visual effects artist in post-production can do several things to enhance the visuals of a film or video. One of the options mentioned, Create a massive explosion, is something that a visual effects artist can do by using computer-generated imagery (CGI) to simulate the explosion and add it to the footage. Another option, Create a Chroma key shot, refers to the technique of shooting footage with a green or blue background and then replacing that background with any other image or video in post-production. This allows for the creation of various environments or settings that may not have been physically present during filming.