WARNING: The following contains spoilers for Shazam #4, on sale now from DC Comics.
Billy Batson's trek through hell to get to the root of his power problems has landed him in the displaced Rock of Eternity. When he entered the legendary location at the conclusion of the last issue, Billy encountered something entirely unexpected: a new version of his old adversary Black Adam.
Now Earth's Mightiest Mortal not only has to deal with how his fluctuating powers are affecting himself but also this future version of Black Adam in Shazam #4 (by Tim Sheridan, Clayton Henry, Marcelo Maiolo and Rob Leigh). While Billy was eventually able to transform from a teen into the grown-up body of Shazam in the last issue, it seems Teth Adam has gone through the opposite transformation. He's no longer a fully grown man - he's a teenager again.
DC's "Future State" titles revealed how Black Adam ended up in the hell bound Rock of Eternity. The "Future State" titles of Flash, Teen Titans, Shazam and the DC One Million back-up story in Future State: Suicide Squad all tied together into one tale, and led directly to this present day story. With all life in the future extinguished by the Unkindness, the Wizard sent DC One Million's Adam back in time to stop it. However, he was trapped inside the Rock of Eternity until Billy discovered him here.
This time-twisting attempt to stop the Unkindness from ever forming is the cause of Billy's power problems here and in Teen Titans Academy. As the Wizard and his power have always been unbound by time, having Adam travel from the future caused the power to fold in on itself and short out. It seems time has also folded in on the future Adam, or Teddy as he asks Billy to call him, and thus caused his magically altered body to revert to a younger form, mirroring his magical journey back through time.
Seeing this scrawny kid version of Black Adam, there is no way that Dwayne Johnson could play this iteration of the character without the aid of some CGI wizardry. To get the DCEU star anywhere close to this form would require something similar to what Chris Evans went through to play the pre-serum Steve Rogers in 2011's Captain America: The First Avenger. Otherwise, he's just far too big to play the short and scrawny Teddy, whose head just meets Shazam's shoulders.
In the end, these power issues are resolved as all of the Wizard's power flows back into Billy, causing Teddy to transform into a regular old man. However, even when old man Adam says the word again, the magic transforms him back into his scrawny teenage self. The two heroes have a lot of work to do before they can restore the Rock of Eternity and prevent the dire fate predicted in "Future State."