In the making of "A World Between Worlds" Dave Filoni comments George Lucas created The Mortis Gods. This makes sense because the Mortis gods first appeared in The Clone Wars series prior to Lucas' sale of Lucasfilm to Disney, so he was still actively involved with the production of that show.
The living portraits of Force characters were first seen in the Star Wars: The Clone Wars season 3, episode 13 story "Overlords."