Season 3 of Supergirl has introduced viewers to a whole new super-team: the Legion of Super-Heroes. Originating in the 30th century, this band of aliens and metahumans have proven to be tremendous allies in the fight against Reign. However, their arc is clearly setting up for the Legion to ultimately go back into cryogenic sleep, and continue their journey back to their own time.
That probably means the Legion's days in Supergirl are effectively numbered. What's more, it's clear that time-travel in Supergirl isn't quite as easy as it is in the Arrowverse. So once they're gone, the Legion are unlikely to come back any time soon. What's next for the Legion?
The Legion of Super Heroes
The Legion of Super Heroes are one of DC's most famous super-teams. In fact, they actually predate the Justice League by two years! They were originally envisioned as supporting characters for Superboy, traveling back in time to meet the Boy of Steel. By the 30th century, Superman's heroism had become a matter of legend. It inspired a group of aliens and metahumans to band together as superheroes, defending their time against terrifying cosmic threats.
The core Legionnaires have always been Cosmic Boy, Lightning Boy (sometimes Lightning Lad), and Saturn Girl. Over the decades, they've been joined by other key characters who've become iconic DC superheroes in their own right; the most notable of these is undoubtedly Brainiac 5, a super-intelligent alien.
DC has rebooted the Legionnaires' timeline twice, and there are promising signs a new version is soon to return in the comics. Every reboot has kept certain consistent themes and ideas, most notably the distinctive Legion flight ring.
How Supergirl has Introduced the Legion
It's long been clear that the Legion exist in Supergirl's timeline. Season 1 saw Kara visit her cousin's Fortress of Solitude, and eagle-eyed viewers spotted a Legion flight ring. It seems that, at some point or another, the Legion will travel back in time and team up with Superman.
Season 2 took two major steps towards introducing the Legion. It introduced two characters associated with the Legion - Lyra Strayd, a refugee from the planet Starhaven, and the Daxamite Mon-El. Both are Legionnaires in the comics, and fans immediately deduced that Supergirl would soon introduce the Legion. No surprise, the season ended with Mon-El forced to leave Earth, and his ship was caught in a temporal anomaly. It wasn't hard to guess that he'd be sent to the 30th century, and become a member of the Legion of Super-Heroes.
The current season has finally introduced the Legion, and revealed that Mon-El was stranded in the 30th century for years. He told others of Supergirl's heroism, and inspired the Legion. Mon-El eventually concluded that he would never return to his own time, and let Kara go. He actually fell in love again, with Saturn Girl. A Legion adventure saw the team blasted back in time, and they were forced to go into cryogenic suspension. They emerged in the present day, and are proving to be valuable allies for Supergirl.
This Could Set Up A Tremendous New Series
The Legion of Super-Heroes have always been popular, and Supergirl is clearly setting the team up for an important role going forward. So far, viewers have only been introduced to three members of the Legion: Mon-El, Saturn Girl, and Brainiac 5. Other Legionnaires are still contained within cryogenic pods, and could easily be awoken as the series continues.
Crucially, though, Supergirl has also set up an intriguing plot for the Legion. It seems that the 30th century is facing a terrible threat, one known only as "the Blight." That may be a deliberate reference to a monstrous creature from the Justice League Dark comics, a gestalt entity formed from all humanity's dark emotions. Or it may instead be a completely new creature. Whatever the case may be, Supergirl has clearly set up a major new enemy in the Legion's own time-period. It seems the entire universe, is threatened by the Blight, and only the Legion can stop it.
It's likely that Supergirl Season 3 will introduce more Legionnaires before this arc comes to an end. It's also set up the potential story for a Legion of Super-Heroes series.