Ray ask Sara if there was a crossover and if they were invited, a breaking-the-fourth-wall joke as the Legends weren't part of the Elseworlds crossover.
Lois told Clark to get home as soon as possible, because of something with "the boys". A reference to the upcoming Superman & Lois series.
When Ray and Ryan mention their respective names for the universe entered by shrinking, Ray points out that there would be copyright issues regarding "Microverse"; this is because it is competitor Marvel's name for their universe entered via shrinking (Legends and other Arrowverse shows are of course DC).
J'onn wears a suit that is similar to the one he wears in the comics.
Rene says to Mick "Rory, huh? We had a Rory once on our team," refers to Rory Regan, the superheroic Ragman.
Marv Wolfman: The "Crisis on Infinite Earths" creator appears as the man who asks Flash and Supergirl for an autograph. He only introduces himself by his first name.