Put creatures moving around in your videos
Looks like standard CGI stuff. It would be easiest to film the musician against a green screen, and then simply replace the background with computer generated scenery and creatures by using a chroma keyer.

He claims that some of the videos were filmed out doors. I don't know whether he's being cheeky or serious. But even if we take him at his word, you need to generate the creatures in the computer and then composite them into the scene. 

In order to make this look good, you need to make sure that the lighting on everything looks correct. If you film the musician against a green screen, you can either put lights on the talent before filming and make sure they match the generated background, or add them in post to match the generated background. It's probably easier to do it during filming.