Final Crisis: Legion of 3 Worlds - Foreshadowing

Foreshadowing

The term "Legion of 3 Worlds" was previously used by Superman during "The Lightning Saga" crossover. Superman used the term to describe "one of the Legion's greatest adventures." He stated that the full story of this event went undocumented because none of the Legionnaires remembered exactly what had occurred. Brainiac 5 later mentions that the adventure involved the Tornado Twins. The Legionnaire Star Boy (then a present-day member of the Justice Society of America under the name Starman) alludes to this encounter, saying that he met "another Thom and another Thom", and briefly mentions the Post-Zero Hour speedster XS, stating that she harbored a crush on Superman.

Geoff Johns revealed in an interview that XS will be appearing in Legion of the 3 Worlds and made it clear that this series, and The Flash: Rebirth mini-series, which he is writing with Ethan Van Sciver on art duties, will pick up threads left hanging in the "Lightning Saga" crossover, saying "Obviously, one of the big things in 'Lightning Saga' that we still haven't addressed is the lightning rod and what that's all about. That will be a central focus of the series."

In Action Comics #864, Batman references the appearances of the different Legions in the present (the original pre-Crisis on Infinite Earths team, the post-Zero Hour incarnation, and the "Threeboot" version), and believes that the future is always changing.