With a massive, four-show crossover looming (it starts tonight on Supergirl), something that probably hasn't received quite as much attention as it ordinarily might is the forthcoming batch of midseason finales for Arrow, The Flash, and DC's Legends of Tomorrow.

That's allowed them to sneak some stuff in under the radar, apparently, including a massive status quo shift to The Flash that fundamentally alters the season going forward in a way that's going to overshadow even the events of Flashpoint.

"Flashpoint," for those who joined late, was an alternate timeline created by The Flash when he traveled back in time and saved his mother from being murdered by a supervillain. He eventually figured out that was a pretty terrible idea, and "fixed" time by allowing his mother to die in the season premiere. The story, loosely based on a major comics storyline called "Flashpoint," created ripples of time that have altered events in the lives of Barry and people close to him.

For starters, Caitlin Snow now has powers and a minor personality disorder as Killer Frost, Cisco Ramon's brother died in a car accident that never happened in the pre-Flashpoint timeline, and John Diggle's daughter Sara is now a son, John Jr., who will likely grow up to be the next Green Arrow.

"There's a villain coming up who's another one of the husk villains that was created by Alchemy, so there's that to deal with, but the midseason finale kind of creates a new problem for our heroes that they weren't anticipating -- something that they've never faced before," executive producer Andrew Kreisberg told reporters today at a screening for the Invasion! crossover. "And it's so big we're actually considering changing the saga sell from talking about Flashpoint to talking about that, because that's what's driving a lot of the episodes, actually. Flashpoint won't loom as large as the threat that presents itself in 309."

First, though, they have to survive an alien invasion, and see if Barry and Cisco can repair the rift in their relationship created when Caitlin abruptly revealed the details of Dante's death in last week's episode, "Killer Frost."

(Photo: The CW/Warner Bros. TV)

Arrow, The Flash, and Supergirl will cross over with DC's Legends of Tomorrow this week in "Invasion!" a three-part crossover that starts in the final moments of an episode of Supergirl and then plays through the other series. Based on the 1988 comic book event miniseries Invasion! from Keith Giffen, Bill Mantlo, Todd McFarlane, Bart Sears, and the crossover -- with its marketing title "Heroes vs. Aliens" -- will closely track the plot of that storyline: aliens will be assembled by The Dominators and descend on Earth to bring an end to the "threat" of Earth's burgeoning metahuman community.

In the comics, the Dominion were secretly hoping to build their own super-race, and as a result created a handful of new superheroes in the course of the story.

In the TV version, rather than assembling a loose alliance of dangerous alien races, the Dominators will apparently be mind-controlling the aliens that join them. That's a revelation that suggests even the heroes might be forced to take one another (or at least the alien Supergirl) on at some point in the story.

NEXT: The Flash, Arrow, Supergirl, Legends of Tomorrow Crossover Trailer / First Look At The Dominators / Invasion! Crossover Promo Photos / Potential The Flash Spoiler Spotted On Set / Will Joe West Die During The Invasion! Crossover? / Enter To Win An Ultra-Rare Invasion! Crossover T-Shirt

Supergirl airs Mondays at 8 p.m. ET/PT; The Flash on Tuesdays at the same time; Arrow on Wednesdays and DC's Legends of Tomorrow on Thursdays. All four series air on The CW. The "Invasion!" crossover will air beginning November 28.