In the scene were William (Jack Moore) and Felicity (Emily Bett Rickards) are playing a video game, the game they are playing is a DC Comics video game called Injustice 2
When Oliver returns home, William and Felicity are playing the video game Injustice 2. Green Arrow is one of the fighters you can play as in the game.
In the previous episode when Oliver and Slade first land in Kasnia, the sign behind them states "RESTRICTED AREA WARNING" in English. Throughout the rest of their time in Kasnia, all visible signs use the Cyrillic alphabet of Russia.
When the Dragon destroys John's "steroid" that he uses for tremors, the box reads "Methylphenidate." Methylphenidate is the generic name for Ritalin.