Board Thread:Questions and Answers/@comment-24520051-20170220195430/@comment-24520051-20170420072615

Arise Etrigan is right! In the series bible, they listed some future episode concepts. One featured Zatanna doing battle with Gentleman Ghost. I've also heard that he was supposed to be in TNBA, voiced by someone along the lines of Sir Patrick Stewart, and he was replaced by Klarion, but I don't know if it's true.

Any fan should read the series bible. Just look it up with whatever search engine you use.