Final appearances of the Royal Flush Gang and Paxton Powers.
At several points after Bruce refuses to pay the ransom and while fighting Queen, Kings upper-class accent slips and after the failed ransom his posh mannerisms slip as well (such as "gonna" and "shaddup!") the implication is that he is faking both.
Melanie / Ten has a job working at "Deckard's Kitchen". This is a reference to Harrison Ford's character, Rick Deckard, in the film "Blade Runner". This film, along with "Akira", has been cited as an influence to the set and background design of the Batman Beyond series.