Mr. Freeze's cold gun is a Kel Tec KSG shotgun.
Although not part of the actual episode footage, when originally shown on network television, FOX used the "Mad City" title card at the beginning of this episode.
The quote that Nygma uses while watching Gotham burn is a shortened version of a speech that Georgia congressman Bob Barr used to speak out against same-sex marriage.
Some time before 02/15/2020 Netflix conjoined this episode and the next ( Heroes Rise: Heavydirtysoul (2017) ) and this episode "ends" at about 42:53 on the time line.