Supergirl executive producer Andrew Kreisberg recently advised fans to "bring Kleenex" for the season finale, and tonight's episode may have given credence to a long-standing fan theory that would explain why.
With the introduction of a Phantom Zone Projector in the Fortress of Solitude, it seems more likely than ever that by the end of next week's finale, Mon-El will be stranded in the Phantom Zone, waiting to be discovered in about a thousand years by the Legion of Super-Heroes.
That's been a popular fan theory all season -- that ultimately Mon-El wouldn't stay on Earth or return to the stars with his mother but that he would likely get injured at some point and end up in the Phantom Zone.
In the comics, it was lead poisoning that led Mon-El of Daxam to be placed in stasis in the Phantom Zone, until he could be recovered and cured in the 30th Century by the Legion.
The fact that tonight's episode of Supergirl stressed Daxamites' lead weakness on at least two separate occasions and then revealed that Superman has a working Phantom Zone Projector in the Fortress of Solitude will likely kick those fan theories into high gear all over again ahead of next week's season finale.
Back in December, DC released a video (seen above) detailing their top ten Legion of Super-Heroes stories, couched in the context that with Mon-El appearing on Supergirl, "the Legion of Super-Heroes can't be far behind."
While it's questionable at best for fans to immediately leap to the conclusion that DC All Access has enough of an "in" with the TV side of things to read that line as a solid confirmation, it's also probably naive to assume that DC spending money to produce a video featuring a team that's currently without a regularly-published comic doesn't mean something.
The Legion of Super-Heroes is a team of teen-aged superheroes from a thousand years in the future. Headquartered on Earth, they come from a variety of different worlds and have a variety of different powers (although each of them wields a Legion flight ring, which provides its wearer with a universal translator, the ability to fly, and some other perks).
Inspired by the legend of Superboy, the Legion traveled back in time to recruit Superman as a teenager, and would periodically steal him away to the future to have adventures with them, returning him to Smallville when they were done. At different points, the post-Crisis on Infinite Earths Superboy (Conner Kent) and Supergirl have also been part of the Legion.
Once one of DC's most successful and popular franchises, the Legion of Super-Heroes have suffered quite a bit since the first line-wide continuity reboot following 1986's Crisis on Infinite Earths. At that time, Superman's backstory was modified so that he was never Superboy and the Legion had to modify its own backstory to accommodate, "invalidating" many of the stories that pre-Crisis Legion fans had loved. The character who took Superboy's place in those retroactively-altered tales, though? Mon-El, the Daxamite hero often known as Valor.
While he did have his own ongoing series set in the present day for a while, and participated in the World of New Krypton storyline which also took place in the then-current DC Universe, most of Mon-El's memorable stories have taken place as part of the Legion of Super-Heroes, so when he came on board, many fans wondered whether it was just a matter of time before we would see the rest of the Legion.
That impression was rooted, in part, in the fact that fans have already seen evidence that the Legion not only exists in the world of Supergirl, but has a relationship with Superman. In the season 1 episode "Fortress," Supergirl headed to Superman's Fortress of Solitude for the first time and one of the first things the audience saw was a Legion of Super-Heroes flight ring mounted on a crystal dais inside.
Has anything much changed? Well, not that we know of. Mon-El is adjusting better but still has not quite found a niche for himself on Earth outside of just his relationship with Kara, and he has been exposed to lead (a story point which was fairly quickly abandoned when Jeremiah Danvers pulled the bullet out).
Supergirl airs on Monday nights at 8 p.m. ET/PT on The CW
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