Lex Luthor teams up with Mr. Mind in Shazam! 15 (Nov/Dec 74), which also features a Captain Marvel, Jr story.
The O' Neil, Oskner and Tex Blaisdell tale begins on Earth-1. Luthor has a new weapon, magic-based, which he intends to use on Superman. Before he does, he decides to read a Shazam! comic. He finds the thing ridiculous, but winds up activating the rod while it is aimed at the comic, and ends up on Earth-S.
Luthor shows up at the right time and the right place to watch Captain Marvel defeat Mr. Mind's latest death weapon. Mind escapes from Marvel, and quickly hooks up with Luthor. Luthor and Superman are comic book characters on Earth-S, so Mind already knows who he is.
Together they launch a fairly good scheme to kill Captain Marvel. Curiously, it does not involve inventing anything, which the two often do. Instead they lure Billy Batson to an aquarium and then dump him into a tank containing a hammerhead shark. Being underwater, there is no way for him to say Shazam. But he plays matador with the shark, getting it to smash the glass, and then turns into Captain Marvel.
Mr. Mind gets caught but Luthor uses his wand to return to Earth-1. I do like the way Superman cameos in the very last panel, catching Luthor.
Mr. Mind is next seen in these pages in 1977. For Luthor, this appearance comes between his role in Superman's Pal, Jimmy Olsen the previous year, and a Superman issue that came out the following week.
Bridwell and Schaffenberger turn in the Captain Marvel Jr story, which also uses Professor Edgewise, not seen since Shazam 1.
Edgewise has created a formula that turns paper into a steel like substance. This gets overheard by a thief who Captain Marvel Jr was pursuing. The guy steals the formula and creates a suit of paper armour, and then begins a crime spree.
Edgewise noticed the paper had a weird electromagnetic quality, and it turns out that force repels Captain Marvel Jr. But by constantly staying on the attack Freddy makes the guy use more and more of the formula, which increases the weight of the paper until it is so heavy the guy plunges down and gets stuck in the sidewalk.