The painting of Varian carrying Eugene in panic is similar to Scooby carrying Shaggy.
Rapunzel mentions the previous time she and Varian ventured in the underground tunnels in "The Alchemist Returns".
Rapunzel brings Varian to the chamber of the Demanitus Device and references the time she used it in "Queen for a Day".
Catalina (Red) transforms into her werewolf form for the first time since "Who's Afraid of the Big, Bad Wolf?".