I would like to see the Celestial Toy Maker again. Perhaps he has not shown up again on the series because his motif of being a madman who amuses himself by making other play deadly games is similarly to a lot of other characters--Mr. Myxzptlk in DC Comics, the Grandmaster and Arcade in Marvel Comics, and Trek’s Q, among others--but I think something original could be done with im.
He would play off well (no pun intended) Matt Smith’s more lighthearted Eleventh Doctor.
