Nygma's license plate is RID LVR a foreshadowing to him becoming the Riddler. A more likely interpretation is that it stands for RIDdle LoVeR (riddle lover). Because he loves riddles.
The gang of fake Penguins invading Galavan's party is reminiscent of Bay N' Gold (1997), when at the end of the episode the "Sting Army" came to the ring to confront the NWO and get beaten up, only for the real "Sting", Steve Borden, to emerge from among them and wreak havoc on the heel stable.