"Elseworlds" Part 2 Drops Several Easter Eggs at Arkham Asylum

The 'Elseworlds' crossover took viewers inside the Arrowverse's Gotham City tonight, and it [...]

The "Elseworlds" crossover took viewers inside the Arrowverse's Gotham City tonight, and it dropped some pretty major Easter eggs in the process.

Spoilers for tonight's episode of Arrow, "Elseworlds" Part 2, below!

The episode saw Barry Allen (Grant Gustin), Oliver Queen (Stephen Amell), and Kara Danvers (Melissa Benoist) traveling to Gotham, in hopes of finding Dr. John Deegan (Jeremy Davies) and convincing him to return reality back to normal. This led the trio to orchestrate a rather elaborate break-in to Arkham Asylum, where Deegan seems to work.

During the break-in, Oliver and John Diggle (David Ramsey) walked down one of Arkham's halls -- where they were greeted by some pretty familiar names on the doors. They passed by doors that read "E. Nygma", "P." Isley, "B." Karlo, "O. Cobblepott", and "M. Guggenheim".

Of course, DC fans will surely recognize the first two, as they reference Edward Nygma/The Riddler, Pamela Isley/Poison Ivy, Basil Karlo/Clayface and Oswald Cobblepott/The Penguin, two of Batman's most formidable foes. This marks the Arrowverse's first official reference of either character, something that makes sense, seeing as the universe has primarily had to mention the world of Gotham City in the abstract in years past.

These references to Riddler and Penguin also come about at a particularly interesting time, as all of those characters play or have played a major role on Fox's soon-to-conclude Batman prequel Gotham. With both shows set in drastically different universes, a crossover has been suggested, but never came to fruition, which makes these small references even more significant.

"That whole world, as writers, I worked on Smallville too and [The Flash showrunner] Todd [Helbing] worked on Smallville as well." Caroline Dries, who wrote "Elseworlds Part 2" and is executive producing the Batwoman solo series, told reporters during a recent press screening. "DC doesn't let you say Batman [or] have anything about Gotham."

"We tried so many times. Now all of the sudden, we can do stuff. And for a bunch of geeks like us, you're in heaven and it's trying to figure out what you want to use. But, that was really fun, I think, for everyone."

And as die-hard Arrowverse fans probably know, the third name on the door is a reference to Marc Guggenheim, who previously served as a showrunner on Arrow and Legends of Tomorrow. This past season, Guggenheim has taken on a consulting producer role for both shows, and even penned tonight's installment of "Elseworlds".

All of these Easter eggs, combined with the Bane-esque mask that appears to also be in the facility, definitely prove that viewers should keep their eyes peeled during "Elseworlds".

What did you think of Arkham Aslyum's Easter eggs in "Elseworlds"? Share your thoughts with us in the comments below.

"Elseworlds" will conclude with Supergirl on December 11th at 8/7c on The CW.