8 Reasons Why Superman Should Be In Shazam!
8. A Real Clash For Shazam
Shazam is a super-powerful character with great wisdom, strength, stamina, power, courage, and speed. Also, he can fly.
Currently on the books to serve as the film's primary antagonist is Mark Strong as the character's arch-nemesis from the comics, Doctor Sivana. Sivana is a classic character, but one who is an intellectual match for Shazam rather than a physical one, generally speaking. Past incarnations have heavily painted the villain as the Lex Luthor to Shazam's own Superman-like powers, so it is unlikely that Strong will be able to go toe-to-toe with Shazam in any sort of physical battle.
Superman on the other hand, absolutely could. Shazam and the last son of Krypton share more than a passing resemblance when it comes to their power sets and a fight between the two of them could present a chance to fully show off the extent of Shazam's powers.
Shazam showing off his full powers on anyone else would almost certainly result in said character's death. But Superman can take the punches and even deal them back if need be.