I'm holding out for deep fake de-aged King Tut, Egghead or Louie the Lilac.

This is finally starting to make some sense. Basically, it sounds like Clayface was the original villain for The Batman: Part II, but I'm guessing Reeves found so much to mine with the character that he felt a spinoff movie would instead do the character more justice. Which ultimately became a Mike-Flanagan-written movie that Reeves will only produce. The fact that Reeves then had to pivot to a different villain would also at least partly explain why The Batman: Part II script has taken him so long to write...