In the original cut of the film his spirit latched on to his dead corps but it could no longer contain him, he needed kylo to bring him Rey so that he could feed off of the dyad, he posed himself as a dying man who wanted to pass off his empire to kylo And Rey but would later reveal later reveal his masterplan in the climax of the film. This was apparently changed late in the game to give Kylo more agency by making him the only one that knew of the dyad but this change sacrificed palpatines cunning and turned him into a Bmovie villian