One of the staples for the RPG crowd are mini and/or hidden bosses. Bosses that are hard to find, hard to fight, and are not part of the linear storyline.
I realize that with 6 months to go and most lines pre-recorded that most of the gameplay is locked down this far into development, but I think this would really add to the gameplay with relative minimal effort. They don't have to be neccasaringly a mandatory part of the storyline, and thus, won't negatively effect the turnaround time as much.
Suggestions for hidden bosses are:
Sally Struthers (in her Jabba the Hutt form)
the evil goldfish from a parralel universe (from season 2 "Spookyfish")
Sexual Harrassment Panda
Moses (the Super Friends version with the big red face)
A giant stone Abraham Lincoln
I am sure there are tons of other great choices but those are ones I rattled off the top of my head. There's also a possible issue of copyright infingment with some of the choices (chef in particular), but just rename some of the characters to "dark, darph, derp [chef]" or some other generic name. The fans of the series will know anyway what was meant anyway. I hope the devs read this, and I would like to know what other fans think!
Thanks for taking the time to read this.