This is the 100th episode of Supergirl.
Showrunners Jessica Queller and Robert Rovner revealed in an interview that they wanted both Calista Flockhart and Mehcad Brooks to appear as Cat Grant and James Olsen, but they were both unable to make an appearance due to scheduling conflicts.
Ironically in the base timeline, Pete Lockwood was an anti-alien bigot who died during an alien attack. In the third altered timeline, he became a pro-Kryptonian zealot who killed himself in a vain attempt to meet Supergirl.
Myxflyx and Betamyx are references to 'Netflix' and 'Betamax', respectively. Additionally, 5 seasons of Supergirl are shown on Myxflyx, a reference to the fact that this is the 5th season of the show.
In the dystopian reality where Mxy loses his powers, the hat he and Mon-El retrieve from the DEO is the bowler used by The Hat, Manchester Black's compatriot in the Elite.