First direct references to Poison Ivy and the Riddler in the Arrowverse.
Arthur Brown slightly breaks the fourth wall when, at the end of his recording, he says "We'll be right back after a word from our sponsors". The recording then ends, going into an actual commercial break.
The Quiz Bowl set is on stage 52. 52 is a frequently used number in DC comics, especially since the New 52 comic book relaunch in 2011.