The ambitious four-part Arrowverse crossover, "Crisis on Earth-X," ended tonight with triumph for the team, two weddings, and a funeral. Fans knew the stakes were high when the heroes from Supergirl, Arrow, The Flash, and Legends of Tomorrow launched into a battle with several of their equally-powered and skilled doppelgangers -- purely evil villains who lived in a horrific alternate universe where the Nazis had won and reigned over their Earth-X.
All of the teams were in life-threatening danger throughout the four episodes, including when several of the heroes were teetering on the edge of a mass grave in front of a firing squad. A cold blast from the past, Leonard Snart, swooped in to save the day that time, but it wasn't the only near-fatal moment of the crossover event. It goes without saying that non-powered team members like Felicity and Iris were in constant danger from vastly more deadly enemies, and Supergirl was mere moments away from having her heart cut out to save an over-radiated Earth-X's version of Kara, aka Overgirl.
Despite the ongoing peril for every character, the final death came as a shock for many. In a daring move to open the portal that would allow them to return to Earth-1 and save the world they had been separated from, Martin and Jax opted to split apart Firestorm so they could complete two necessary tasks at once. While trying to flip the switch to open the breach, Martin was shot by Nazis and mortally wounded. Jax reconnected with Martin in an attempt to keep him alive long enough to be helped by Gideon, but the Firestorm link was ultimately more dangerous than helpful.
Those keeping up with Legends of Tomorrow news already knew that Victor Garber was reportedly exiting the show, but much of the season's plot has revolved around the team finding a way to scientifically separate Firestorm so that Martin could go home to be with his wife, daughter, and grandchild. Instead we were blindsided with a dying Professor Stein, whose injuries were also going to kill Jax due to the duo's powerful bond.
In a very moving scene, Martin decided to take a serum created by Wells, Cisco, and Caitlin -- and further enhanced by Gideon -- to "cure" himself of Firestorm. This broke their connection and left Stein to die of his injuries, but saved the young man he considered a son. Unlike some recent character deaths in the Arrowverse, thankfully Martin's selfless sacrifice was shown to greatly affect all who knew him, and his unexpected absence leaves many uncertainties for the Legends team going forward.
Professor Stein has been in the Arrowverse since season 1 of The Flash, first forming Firestorm with Caitlin's former fiance, Ronnie Raymond. After Ronnie's death, Martin needed a new partner to take on the other half of Firestorm, and he and Jax teamed up in that universe before jumping on the time-traveling Waverider with the Legends crew.
The question now is if Jax too is left powerless, or if he'll require a new partner to bond with to still be Firestorm. While we don't see him jumping on that "sticky spider" serum Stein had cooked up for him, there's always a possibility Jax may acquire some different powers in the future. Whatever happens with the destiny of Firestorm, Jax will be suffering from the loss of a psychically-bonded friend and important father figure in his life, and there's no telling how the rest of the team will do without the professor's incredible intellect and calming, rational influence on their largely wilder natures.
The four Arrowverse series will return with their midseason finales next week on The CW, beginning with Supergirl at 8pm on Monday, continuing with The Flash on Tuesday at 8pm, DC's Legends of Tomorrow following at 9pm, and Arrow on Thursday at 9pm.