The lines between "Arrow" and "The Flash" have blurred before, but this week's CW crossover event is bigger, bolder, and better integrated than ever.

Moviefone previewed the massive superhero merger, which sets the stage for the network's upcoming spinoff "Legends of Tomorrow" and will air over two nights this week. The story follows Teams Flash and Arrow as they try to protect two new heroes, Hawkgirl and Hawkman, from a brand new villain in Vandal Savage.

According to the showrunners who answered questions after the screening, putting it all together was one hell of a challenge.

"I don't think its possible to overstate the incredible amount of difficulty it was for just about everyone involved," Marc Guggenheim, executive producer of "Arrow" and "Legends of Tomorrow" told Moviefone.

"We love that kind of challenge," Greg Berlanti, co-creator of all three series, added. "You can try and guess how large it's going to be, but you don't really know until you're in it."

"It was an acting marathon," Falk Hentschel, who makes his first appearance Tuesday as Hawkman, said.

In the end, everyone's hard work on "The Flash"/"Arrow"/"Legends of Tomorrow" crossover event paid off. The action in the two-part episode is riveting, the effects are spectacular, and the danger is palpable. There are tears, laughs, and oh so many sets of sprouting wings. Here are nine things to look forward to when you watch the episodes, titled "Legends of Today" and "Legends of Yesterday," respectively.

1. Vandal Savage is a timeless, totally cool villain.
Move over, Damien Darhk -– there's a new magical badass in town.

Vandal Savage (Casper Crump), an immortal, knife-wielding assassin, shows up in Central City hot on the trail of Cisco's (Carlos Valdes) new girlfriend Kendra Saunders (Ciara Renée). When Team Flarrow tries to shelter Kendra from Vandal's 4,000 year old storm, they get more than they bargained for. Far more than competent villain, he is also a dryly funny dude who won't hesitate to boast about prior encounters with folks like Harry Houdini and Robin Hood. Did we mention he's destined to become the main bad guy on "Legends?"

2. Hawkman and Hawkgirl have arrived!
Vandal Savage isn't the only "Legends of Tomorrow" mainstay introduced on this week's two-parter. We also get the debut of Carter (Falk Hentschel), aka Hawkman, as well as Kendra's first emergence as Hawkgirl. What's their relationship like?

"They come as a team," Hentschel explained. "In my mind they're like a bickering old couple. He's gone through 4,000 years of loving her and having him loving him back... but he's terrified always of losing her."

Two new superheroes also means two new superhero costumes. Putting on Hawkman's outfit was "like a dream come true," Hentschel revealed. "It was awesome." But sadly that means...

3. Cisco finds himself neck deep in an Ancient Egyptian love triangle.
"The Flash" hasn't had a bonafide love triangle since Eddie was killed off at the end of last season, but all of that changes when Hawkman crashes the party and gets between Kendra and Cisco, who had quietly become the show's cutest couple. We won't spoil what happens, but considering Kendra and Carter have been soul mates for over 4,000 years and will soon be flying off to join "DC's Legends of Tomorrow," it's safe to say Cisco is fighting an uphill battle.

4. The crossover will give us unexpected character pairings.
One of the best things about these crossovers is that they allow the showrunners to mix and match characters who don't often share the screen. Barry and Felicity, for example, haven't interacted much since their Season 1 date, but the crossover reunites them and allows fans to see how their relationship has evolved after so much time apart.

5. And Team Arrow's perfect reaction to the existence of a multiverse.
Another natural consequence of these intertwining stories is an exchange of information between Team Arrow and Team Flash, as the two groups spend time catching each other up on what they've been doing. Watching old friends reminisce might not be entertaining in real life, but when you're dealing with superheroes, magical villains, and alternate dimensions it actually makes for great TV. Can you guess which character learned about the multiverse then immediately wondered whether Oliver's doppelganger might be potbellied and bald?

6. There will be double the funny.
"The Flash" has relied heavily upon comedy since its inception and more recently "Arrow" has made strides along those lines, too. So, it shouldn't come as much surprise that this week's two-parter is filled with jokes -– and these are some of the funniest yet. From Cisco trying to rename one of the Team Arrow heroes to Oliver complaining about how everything looks brighter in Central City, the humor (and meta-humor) is on point.

7. And pop-culture references aplenty (even an "Avengers" one!).
By now "Flash" fans know Cisco has never been one to shy away from a good pop-culture reference, but this week he's joined by Felicity and even Thea as they name drop more movies and TV shows than ever before. From Indiana Jones to "Highlander" to "Game of Thrones" to "Lord of the Rings," they pay homage to all the classics, new and old. Most shocking is a perfectly timed "Avengers: Age of Ultron" shout-out, which seemingly serves as proof that Marvel movies do indeed exist in this version of the DC universe.

8. Oliver will be asked to keep a secret from Felicity, and will eventually find comfort in the arms of another.
Green Arrow has been all about honesty and transparency this season, so when an unexpected character asks him to keep a secret from everyone, including his lady love Felicity, his resolve is put to the test. What does he do? We're not going to ruin that surprise for you, but we will say that he's lucky to be surrounded by so many supportive friends and family. One of them even gives him the most awkward hug ever during the episode, which made us laugh out loud.

9. The mother of all flashbacks.
"Arrow" is no stranger to exotic flashbacks, but this week takes us further back and perhaps farther away than we've ever gone before. If you've seen the trailer you probably noticed Hawkgirl, Hawkman, and Vandal Savage butting heads in Ancient Egypt, where their sad and twisted story begins. The production design for the flashbacks is exceptional.

That's great news considering time travel and period-set stories may be a central component of "Legends of Tomorrow."

"Part of the fun of 'Legends' is that it takes place all throughout history, future, and past." Guggenheim said.

The CW crossover event begins Tuesday at 8 p.m. with "The Flash" and concludes on Wednesday at 8 p.m. with "Arrow."