Adventure 357 (June 1967) has a pretty decent mystery story by Jim Shooter, with Curt Swan art. It manages to play both sides, with a phony ghost and a real one.
The Legionnaires are feeling guilty over Ferro Lad`s death, many of them having bad dreams. And then deadly accidents begin to occur, with ghostly messages left behind. They decide the Clubhouse must be haunted, and Princess Projectra holds a seance to try to contact his ghost.
Brainiac 5 is not at all impressed with her oracular background, the first tension between him and a magic user on the team.
She manages to contact Ferro Lad`s ghost, who insists that he wants vengeance against the four members who `let him die,`and demands that the Legion disband.
Brainiac 5 orders this to happen, and they go their separate ways, but almost immediately after Superboy is snatched by a Controller. This is the first time the Controllers appear in any DC book. There is as yet no backstory linking them to the Guardians of the Universe, but we do learn that the one in the tale was responsible for the creation of the Sun-Eater, which he planned to use for conquest. It is the Controller who created the ghost of Ferro Lad, and wants revenge on the Legion.
Superboy`s flight ring gets activated by a mysterious force, which summons the rest of the team, who free Superboy, while the same force, revealed as the true ghost of Ferro Lad, takes down the Controller. Nicely done for a dead guy.
This story also features a brief appearance by Cosmic Boy`s younger brother and future Legionnaire, Pol Krinn.