During Mayor Penguin's party at the club, the band is playing a modified version of the theme song from "The Batman" - the animated show that ran from 2004-2008.
Michael Stoyanov, the Red Hood Leader, is no stranger to being in a gang in the Batman universe. He was in Joker's gang as Dopey, in the opening bank robbery scene in The Dark Knight (2008).
There are a couple scenes where you can see Mayor Cobblepots shirt cuff. There is an umbrella stitched on it, the Penguins trademark
This mark's the second appearance of the Red hood gang.
This series marks the 4th time the Penguin runs for Mayor of Gotham, having done the same in the Adam West 1960s series, Batman: The Animated Series and Batman Returns.