Warden Page 413 (Patreon)

This is what Insight is able to see when the Prisoner is using the Mind Bridge. On the inside there might be trippy visions showcasing the inner thoughts of those taken, but True Sight isn't a spell that allows someone to see inside of the mind. It only allows for interpretations of external phenomena. Which once again underlines that the Prisoner has a penis dragon as an avatar and that his mana causes him to literally glow with power.