The Alura hologram tells Kara that she possesses the accumulation of knowledge of the 28 known galaxies. This is the same thing that the Jor-El hologram told Superman in Superman (1978).
Samantha mentions once working in Central City. Its Earth-1 counterpart is where Barry Allen resides on The Flash (2014).
Reign's heat vision is red, a reference to the traditional color of Kryptonian heat vision.
Imra Ardeen represents Saturn Girl in the Legion of Superheroes.
Chad Lowe returns as Thomas Coville from "The Faithful (2017)", which was the first time Samantha's identity as Reign was alluded to. Lowe also directed "Wake Up (2017)", which ends with Sam acquiring her abilities.