Stuart Fails To Save The Universe Brings Mayim Bialik Back As A Very Different Amy — Plus, Why You Didn't See Flash Battle Mr. Freeze

"Stuart Fails to Save the Universe" welcomed Mayim Bialik back for a second time in Episode 9 — and once again, Amy Farrah Fowler was living a very different life.

Bialik first appeared in Episode 4 as an alternate Amy who served as Stuart's psychiatrist after he was institutionalized in a Pleasantville-like universe. In the HBO Max comedy's penultimate Season 1 adventure, viewers encountered yet another version of Amy — this one married to the Golden Age Flash (played by Andy Ridings).

Her return came as Stuart, Denise, Bert, and Kripke found themselves trapped in a DC comic, traversing Gotham City and Central City in their ongoing quest to save the multiverse. (Fellow franchise alum Riki Lindhome, who played Ramona Nowitzki and previously appeared as a Caltech receptionist in Episodes 2 and 7, once again resurfaced — this time as a Gotham City flight attendant.)

For co-creators Chuck Lorre, Bill Prady, and Zak Penn, the episode offered an opportunity to fully immerse themselves in a setting that the characters of "The Big Bang Theory" spent 12 seasons obsessing over.

"Zak is a huge comic book guy," Prady tells TVLine. "What was a lot of fun was being in a room with Zak while we were writing that, where he had all of these facts immediately, readily available."

But rather than focus exclusively on the larger-than-life heroics, the writers were particularly interested in exploring the more mundane corners of that universe. "The kinds of things that the guys would have nerded out about, like where is Gotham City and stuff like that," Prady explains. "[We got] to have Stuart have that knowledge and then exist in that world — but exist in the ordinary, dull parts of the world."

"That's what excited all three of us," Penn adds. Hence the episode's secret superhero closet, the airport delays, and, as Lorre recalls, "rugelach and Dr. Brown."

That approach also produced one of Lorre's favorite jokes of the episode: "One of my favorite moments in that was Stuart narrating a battle at super speed between the Flash and Mr. Freeze [played by Eric Allan Kramer], and you can't see anything because he's running so fast... and [because] we didn't have the budget to actually shoot that."

"It's radio," Prady quips. And for him, that sequence exemplified the episode's larger effort to play with the conventions of comic-book storytelling.

"I like when Kripke says, 'Comic books are action packed. How is waiting at an airport part of a comic book?'" he says. "And it is the fascination with, you know, 'What happens in those worlds on non-exciting days?'"

Of course, Stuart and Co. eventually found their way out of the DC comic. With an assist from the Golden Age Flash, the quartet returned to the comic book store — only to discover that their home base was now trapped in some sort of void of nothingness.

And with that ominous reveal, the stage is officially set for the September 24 season finale.