Clayface as a makeup artist / actor could be a great mystery story.
Imagine all the mind-blowing reveals, that like a dozen characters throughout the movie were all played by the same guy underneath.
They could go nutty with the marketing too. Not announcing Clayface is involved (maybe using Hush as a red herring or something), or “casting” an actor that doesn’t even exist with a fake IMDB, someone doin the press tours that’s secretly Jeremy Strong or Mahershala Ali underneath.
Also I would perhaps amalgamate Clayface with Croc. A guy with a skin condition (nicknamed Croc in his youth) who, in his desperation to cover up his condition, ended up becoming a makeup/prosthetic expert, eventually becoming so proficient that he would use it create entirely new faces (thus simultaneously learning to “act” and become other people), finding work in the movie business like Mike Marino, and eventually using his skills on himself to create an actor persona Basil Karlo, who ends up taking off and entering all the sketchy Diddy parties of Gotham (set up for the Court of Owls). At some point his makeup runs (like clay) to everyone’s horror and he’s cast out, thus turning to a life of crime, and at some point takes more permanent measures to fix his face (reconstructive surgery ala Hush), or perhaps, he’s after the Court’s anti-aging research (fear-based experiments conducted in Arkham to extract adrenochrome? Google it), somewhere along the line framing Bruce to get him thrown in Arkham to help Jones get what he wants.
Whatever they do, I think a villain that delves into the themes of self-acceptance and fear of vulnerability would be fitting for Bruce at this stage. Joker imaginably would be a great parallel for both characters too, the guy born with a messed up face but found “contentment” in who he is without having to hide.