“It's Always Sunny in Philadelphia” cast wrecks havoc on“ Abbott Elementary” in crossover promo

Abbott Elementary won't know what's hit it.

In the newly released promo for the epic crossover between Abbott Elementary and It's Always Sunny in Philadelphia, the Paddy's Pub Gang is up to no good.

The promo shows Janine (Quinta Brunson) welcoming Charlie (Charlie Day), Dee (Kaitlin Olson), Dennis (Glenn Howerton), and Mac (Rob McElhenney) to the school. "Oh, is that what this is?" Dee retorts in response to Janine's greeting.

Related: Abbott Elementary's top secret crossover episode revealed to be with It’s Always Sunny in Philadelphia

The Gang, as they are fondly known, come to Abbott as volunteers sent by the district. But it goes about as well as one might expect. Mac is making what appear to be sexual advances at Ava (Janelle James) — and really, would we expect anything less? Frank (Danny DeVito) and Mr. Johnson (William Stanford Davis) spar, each calling each other "trash" and the "sheriff of trash."

Things appear to escalate until the scoreboard crashes to the ground in the gym and Dennis walks away, pretending he didn't see anything.

"It's always funny in Philadelphia," the promo promises, teasing the episode.

Related: Talia Shire cast as Melissa Schemmenti's mother on Abbott Elementary after Bette Midler pleaded for role

The episode is perhaps the most highly anticipated of Abbott's fourth season, with creator and star Quinta Brunson teasing it back at San Diego Comic-Con last summer. "We will be doing an interesting crossover this season," she hinted. "But I’m not gonna tell you with who or what or when, but it will be exciting, and I think it will change television as we know it."

Many immediately speculated that it could be with It's Always Sunny, given the shared Philadelphia setting and the importance of the city to both shows' universes. Additionally, both shows' creators had expressed a desire for a crossover event on social media in the past. They officially announced the special episode back in October.

Related: Quinta Brunson wants Daniel Radcliffe to play Mr. Johnson's son on Abbott Elementary

But the FX R-rated comedy and the primetime network sitcom aren't necessarily a natural pairing. "I will just say that when [Quinta] came to us with it, I was like, 'How are we going to make this work?'" producer Justin Halpern previously told Entertainment Weekly. " I was really excited about it, but I was like, 'I do not know how this is going to work.'"

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Audiences will find out how they figured that out when the episode airs on ABC on Jan. 8.

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