Tonight's episode of "Arrow" is a special one for two reasons -- not only is it right in the middle of the "Invasion!" crossover, unfolding this week between "Supergirl," "The Flash," "Arrow" and "DC's Legends of Tomorrow" -- it's also the 100th episode of the DC Comics-based series that spawned the "Arrowverse" back in 2012. Thus, the creative team behind the show had to figure out a way to do justice to the landmark number, while also moving the larger story forward.

"That was the challenge," "Arrow" executive producer Marc Guggenheim told press including CBR during a Q&A this week at The CW's Burbank headquarters. "How much to service the 100th episode-ness, and how much to service the crossover? I think it's pretty obvious that we chose to go 100th episode. It was totally a challenge. It was Greg [Berlanti]'s idea to have our five "Arrow" people enter the Dominator matrix, and that sort of allowed us to have our cake and eat it too."

Guggenheim and company's solution for having and eating that cake came in the form of the five "Arrow" cast members past and present -- Green Arrow (Stephen Amell), Diggle (David Ramsey), Thea (Willa Holland), White Canary (Caity Lotz) and the Atom (Brandon Routh) -- being abducted by The Dominators, the alien antagonists of "Invasion," at the end of last night's episode of "The Flash."

When tonight's "Arrow" picks up, the five are held in pods by the Dominators and experience a shared hallucination; a window into a world with no aliens and no metahumans, and where Oliver never became the Arrow. Oh, and he's engaged to Laurel, played by the returning Katie Cassidy, who left the show earlier this year after her character was killed off towards the end of season four.

"This is sort of Oliver's version of 'Flashpoint,'" Guggenheim said, referencing the DC Comics-inspired "Flash" storyline where Barry Allen (Grant Gustin) changed the timeline by saving his mother from being murdered by the Reverse-Flash (Matt Letscher). "It's a little bit Oliver's version of 'For The Girl Who Has Everything' from last year's Supergirl. There's a reason why these stories are iconic and familiar tropes. When you show the protagonist the path not taken, and you basically put them in the situation where they can choose to stay on that path, or go back to their life with all of its ugly aspects and challenges, and they choose the selfless choice of returning to that ugly past, it makes your character stronger."

"Arrow" airs at 8 tonight on The CW; the "Invasion!" story concludes this Thursday at 8 p.m. with the latest episode of "DC's Legends of Tomorrow."