Second of four appearances of the time-traveling science fiction author H.G. Wells.
In the original broadcast episode, when Lois is flying with the parallel world Superman, R.E.M.'s "I am Superman" is played in the background. In the DVD version, however, the song "I want to be Superman" is played.
Though never called a "multiverse" in this episode, it's the first mention and appearance of a parallel earth in the series. Since the producers of the CW's "Crisis On Infinite Earths" have stated that pretty much every live action iteration of a DC Comics property exists in the CW's "Arrowverse", this would be one of the multiverse's earliest appearances, though not its first (its first appearance would actually be in an episode of "Superboy").
Tempus refers to Clark as a "mild mannered reporter for a great metropolitan newspaper." The same phrase was used to describe Clark in the Fleischer Studios / Famous Studios series of animated shorts which began with Superman: The Mad Scientist (1941).
Winrich Kolbe previously directed Through the Looking Glass (1995), which likewise involved a character being brought to a parallel universe against their will and impersonating their deceased (or presumed deceased) counterpart.