The ending of Crisis on Infinite Earths "Part Three" suggests that Supergirl will take the spotlight in the next chapter of the Arrowverse crossover, despite the fact that it will air as an episode of Arrow. It appears that characters from Supergirl will factor heavily into the conflict with the Anti-Monitor (LaMonica Garrett) for the remaining two episodes of the crossover event, which airs in January.
So far, The CW has aired three installments of the crossover (Supergirl, Batwoman, and The Flash), with only two chapters left. The Arrow and Legends of Tomorrow episodes will air together as a two-part conclusion on January 14. In the last episode, the Anti-Monitor's antimatter cannon was destroyed by a heroic sacrifice from Earth-90's Barry Allen (John Wesley Shipp), but this was far from the end of the Crisis. The Anti-Monitor unleashed his secret weapon, a mind-controlled Harbinger (Audrey Marie Anderson), against the heroes and succeeded in completing the destruction of the Infinite Earths. At the last second, Pariah (Tom Cavanagh) teleported the seven paragons to safety.
Following the massive cliffhanger in hour three of Crisis on Infinite Earths, it appears that eight heroes are left to fight the Anti-Monitor (six of which being the Monitor's paragons). One of the seven, Earth-96's Superman (Brandon Routh), was killed and replaced by Supergirl's Lex Luthor (Jon Cryer). The final hero is Oliver Queen (Stephen Amell), who was transformed into Spectre from DC Comics. As for the six paragons chosen to save the multiverse, four of them are the main protagonists of the Arrowverse shows, The Flash's Barry (Grant Gustin), White Canary (Caity Lotz), Supergirl's Kara Danvers (Melissa Benoist), and Batwoman's Kate Kane (Ruby Rose). Two more are Supergirl's Martian Manhunter and the new Crisis character, Ryan Choi (Osric Chau).
Of the remaining eight heroes in the Arrowverse, three of them are strangely from Supergirl. Since the next episode will likely focus on the six paragons, Lex Luthor, and Oliver trying to beat the Anti-Monitor, it appears that the Arrow episode of "Crisis" will feature an unusual amount of representation from Supergirl.
Lex Luthor and Martian Manhunter will both play roles in the upcoming battle, with the supporting casts of all the other Arrowverse shows being relegated to the sidelines until they can be brought back. The only Arrow character aside from Oliver who may factor prominently in "Part Four" is Lyla, who is currently on the side of the main villain. Since the Anti-Monitor has succeeded in destroying the multiverse, these eight characters are the only ones with a shot at reversing the events of the Crisis.