Ok so here's the cast so far:
Mark Hamill is Joker and Swamp Thing
Kevin Conroy is Batman and Plastic Man
Deidrich Bader is Booster Gold
James Woods is Lex Luthor
Joanne Spracklen (who?) is Supergirl
Carl Reiner is The Wizard
Brent Spiner is The Riddler
Tara Strong has also been cast but dunno her role yet. Probably Barbara Gordon/Batgirl
http://www.newsarama.com/28399-star-...e-riddler.html