1) The redesigns of Riddler, Mad Hatter, the Ventriloquist (his head looks like an eraser), Baby Doll, and Killer Croc.
2) Talia's new voice
3) Farmer Brown
4) Cutting Mr. Freeze's story out of Holiday Knights (I know, it wouldn't fit, but still...).
5) Mr. Freeze's henchwomen
6) Joker's "Three Stooges" henchmen