Arrow picked one hell of a week for its 100th episode, landing smack-dab in the middle of The CW’s four-way superhero crossover with Supergirl, The Flash and Legends of Tomorrow. Still, we’ve time yet before the heroes come together, for which producer Marc Guggenheim reveals not only what brings Supergirl to Star City, but also what other familiar faces will pop up for Arrow’s centennial.

Where previously we’d learned that The CW opted not to fold the Supergirl universe into the same dimension as its CW counterparts, merely crossing Kara over for the three-part (yes, three) event, Arrow boss Marc Guggenheim offered new details at a recent press screening (via EW). For one, it seems The Flash will naturally bridge the gap with Supergirl at the tail end of her episode that week, as Barry and Cisco call on Kara’s help:

Once the heroes realize that they’re up against aliens, they decide that they need an alien on their side. Fortunately, Barry knows a really nice one. I don’t think it’s a big shock that between Barry and Cisco, and all their experiences with Earth-2 and the multi-verse, that they can pluck her from Earth-CBS.

As to Wednesday’s Arrow portion of the four-way crossover, Guggenheim assured that the series would still find time to plumb the depths of its own history:

When the news broke that the 100th episode was also going to be the crossover episode, people were up and down my Twitter and Greg [Berlanti’s] Twitter I think, in this case, in a very positive way. People didn’t want to feel like the crossover was highjacking what should be a really seminal episode and a seminal moment for the show Arrow, which I think is wonderful. Greg came up with an idea that really does allow us to have our cake and eat it, too.

We’d perhaps guess that involves some form of time-travel (or dream sequence?) to accommodate the vast array of returning characters, from Jamey Sheridan and Susanna Thompson’s Robert and Moira Queen, to Deathstroke and Katie Cassidy’s Laurel Lance. Also joining the fray will be John Barrowman and Neal McDonough in their roles as Malcolm Merlyn and Damien Darhk, which we’d also guess is no coincidence with their roles among Legends of Tomorrow’s Legion of Doom.

It could be a few weeks yet before Arrow, Flash, Legends and Supergirl really let fly with the crossover teases, but will Arrow feel represented enough in its 100th hour?

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