Sister's Bride
Welp, just had the stupidest thought...what if Supernova actually thought the 'one of their kind' is actually Dark Side/Batman? I know, I know, Supernova could have most likely meant a Dream Seed and likely Batman made a lot of visits with tickets in hand to those he can reach, but it's hard to ignore a bunch of supposed superheroes watch a superhero movie and Supernova is arrogant enough to think he can control Batman and The Joker or he may have skipped the part that Flash revealed that Dark Side is Batman or some other thing he thinks is beneath him.