"Dennis is the key" to the Abbott Elementary/Always Sunny crossover, creators say

Crossing over comedies as disparate as Abbott Elementary and It's Always Sunny In Philadelphia wasn't as difficult as you'd think: Disney head honcho Bob Iger was "very into it" when Quinta Brunson pitched him the idea, she says in a new interview with Rolling Stone. Creatively, "I think it got unlocked when we realized we could tell the same story from two different perspectives," Rob McElhenney adds. "So we have the Abbott episode and then the same story, except told through the prism of Sunny, which will air four or five months later." 

Specifically, the fact that Abbott is a mockumentary and Sunny isn't "allowed for us to still be authentic and step into the world of Abbott because these characters are going into a school and they’re constantly monitored by cameras, so they would put on an act," McElhenney explains in a separate interview with The Los Angeles Times. "If we’re not acting the way that our Sunny characters would, it’s because we know we’re being filmed and we’re putting it on the show. We might not use the same language. We might not make our intentions so obvious or known. We might not be wearing our id on our sleeves. Conversely, when they came over to us, we thought it would be fun to see what their characters would be like when the bell rings and the cameras are not on them."

Both actor-creators sound delighted about the chance to play against some of the funniest characters on television; McElhenney immediately requested to have a storyline with Janelle James, while Brunson declares her scene partner Kaitlin Olson is "one of the most underrated comedic actresses. I think people should talk about her every single day." She teases that the Sunny crew have done something "masterful" with Sweet Dee, so that watching the FX episode after having seen the ABC episode "adds another layer to all of this." 

Another layer that requires viewings of both episodes to fully understand is the plotline involving Dennis (Glenn Howerton). It may not be fully clear when the Abbott Elementary half airs on January 8, but "Dennis is the key," Brunson teases to the L.A. Times. "Yes," McElhenney agrees. "So when you see the “Sunny” episode, you’ll realize why we did that with Dennis."