Lightning Lass's twin brother, Lightning Lad, is mentioned by Barry Allen's daughter Nora in "Nora (2018)", in which she considers his lightning bolt to be less cool than Barry's, and he appears as a member of the Legion in Smallville (2001)'s "Legion (2009)".
Winn mentions that Chemical King and Lightning Lass are members of the Legion.
This episode was the least watched in the show's history, down 150,000 viewers from Part 1. While the three-week hiatus had an effect, the heavily promoted possibility of Kara and William getting together, fan favorite Lena continuing towards the path to villainy, and Lex seemingly taking over the show have been identified as reasons why viewers tuned out.
Before Brainy charges into battle, he screams "Leeroy Jenkins!" This references a much watched World of Warcraft video where a player named "Leeroy Jenkins" yells his name and charges into a room full of enemies, ending with the whole party being killed. Thus when gamers are about to do something ill-advised, they will often yell "Leeroy Jenkins!"
Nia doesn't appear at all.