When Eugene, Lance and Maximus are being chased by a large boulder is a reference to Indiana Jones and the Raiders of the Lost Ark.
Varian is comparing two metals: iron and steel. But iron is one of the major components of steel.
There are several sequences that reference scenes from "Secret of the Sun Drop", besides, Cassandra's actions are also similar to Varian.
When Varian says "Demanitus, you genius" during the episode is similar to the way Rapunzel said "Pascal, you genius" during the episode No Time Like the Past.