Billy Batson having a crush on Wonder Woman comes from the "Power of Shazam" comic. That comic also had the Wizard communicate to Billy through a dream, where his face was on Wonder Woman's body.
Though the Daughters of Atlas were drawn from Greek mythology, they have no precedent in DC Comics lore. This is the sixth DC movie with wholly original villains, after Superman and the Mole-Men (1951), Superman III - Der stählerne Blitz (1983), Supergirl (1984), Steel - Der stählerne Held (1997), and Catwoman (2004).
Darla adopts a pet kitten, which she calls Tawny. In the comics, Shazam had a talking tiger friend named Tawky Tawny.
Steve the Pen is based on the Historama, a device the Wizard possessed in the comics that could reveal to him the past, present and future. The comics had this device be a TV screen and later a book.
Grace Caroline Currey, who plays Mary Bromfield, also plays her superhero form, replaced Michelle Borth from Shazam! (2019). According to director David F. Sandberg, Currey is now playing both parts but her hair and makeup are slightly different when she's super so her "normal" identity is kept safe.
Michael Gray: a previous live-action Billy Batson from Shazam! (1974), appears as a bystander in the final battle. Gray not only has on a red and yellow shirt, his costume from that show, but he calls Shazam his original title of "Captain Marvel".
Natalia Safran: wife of producer Peter Safran, appears as the driver with kittens. She appears alongside her daughter Lou Lou Safran.
Lotta Losten: Wife of David F. Sandberg appears as the first person Shazam saves on the collapsing bridge.