Captain Boomerang (George Harkness) has super-speed in this game. This is a trait used by his son Owen Mercer (the second Captain Boomerang), who was a superhuman in contrast to his normal father.
It has been clarified by Rocksteady that this game takes place in the same universe as the Batman Arkham games (aka the Arkhamverse) and references several events from Batman: Arkham Asylum (2009), Batman: Arkham City (2011), Batman: Arkham Origins (2013), Batman: Assault on Arkham (2014) and Batman: Arkham Knight (2015).
First Rocksteady DC game that is targeting the M rating. Batman: Arkham Knight (2015) was rated M, but it was not intended by the developers.
Rocksteady say that the reason Deadshot is black in this game is that the previous one had stolen his identity. Though fans assume that the change was due to the popularity of Will Smith's role as live action Deadshot in Suicide Squad (2016).
Earth-2's Justices League statues has Bruce Wayne/Batman, Barry Allen/Flash, Hal Jordan/Green Lantern, Supergirl/Kara Zor-El and fifth unknown hero.