In this travels with youngling Grogu, Luke tracks a long lost Jedi master to a planet that is shrouded in the dark side of the force.
Details: The former Jedi High Council member Oppo Rancisis used the dark side energy of the planet Domond to hide himself from the Empire. As years went by the evil feasted on the Jedi Master turning him into a tool of the dark side.
Luke, unwittingly, trains in the dark side under Rancisis before the planet reveals itself, turning Rancisis into an apparition of the Dark Lord of the Sith, Darth Bane.
Lukes first hand exposure to the dark side had long term effects on him and contributed to his visions of Ben Solo.
