Season four of The Batman is a damn fine season if I do say so myself. They cut back on Joker/Penguin episodes and introduced Robin, Kill Moth, Clayface II (Basil Karlo), Black Mask, Harley Quinn, and Martin Manhunter. Not to mention the "Artifacts" episode which pays heavy tribute to The Dark Knight Returns (with appearances by Nightwing and Oracle), Penguin starting up a Injustice for All Gang in "Team Penguin", an all out battle royal between Batman/Robin and his entire rogues gallery in "Rumors", and at the end of "The Joining Part 2",
. I only hated one episode in that season and that was "The Everywhere Man" episode. Besides that - good season from beginning to end.
EDIT - Oh and Kevin Conroy (as John Grayson) and Mark Hamill (as Tony Zucco) reunite in "A Matter of Family".