This marks Jesse L. Martin's return to the series after his back injury during the summer hiatus. He was last seen in News Flash (2018).
After the battle between King Shark and Grodd, Cisco states that it was the best "Kaiju" battle ever watched, a reference to Godzilla and King Kong etc.
Joe texts Iris saying, "but Grodd hate banana", which is a reference to the S1 episode Grodd Lives (2015) wherein Grodd kidnaps Joe and Joe tries to give him a banana, which Grodd refuses, as he detests them.
This episode was subtly foreshadowed in Attack on Central City (2017); after Grodd was defeated and was mentioned to have been locked up at A.R.G.U.S., Caitlin stated that he can be thrown into the same cage as King Shark for all she cares, since any good in him is long gone. Cisco then states that was a fight he'd pay money to see.
Grodd has not been seen in Central City since "Attack on Central City", since he was transferred to "Legends" for the 2017-2018 season. He was last seen in early 1990's Zambesi in "Guest Starring John Noble".