The 'Abbott Elementary' EPs talk jokes cut from 'Always Sunny' crossover, including backstories for Frank and Mr. Johnson.

It’s always busy for the It’s Always Sunny in Philadelphia cast.

Compendio: Frank is established as Dennis and Dee’s father when he first appears in Season 2 of "Always Sunny" — though the audience later finds out that he is not their biological father.

Charlie learns to read, Dee impersonates Ben Franklin, and Frank fights raccoons. We don't quite know what's up with Dennis though.

It's Always Sunny in Philadelphia is about to release ... However, the best character pairing was Frank (Danny DeVito) and Mr. Johnson (William Stanford Davis). These two are a natural fit because ...

We always knew that It's Always Sunny in Philadelphia's Frank (Danny DeVito) would easily match Abbott Elementary's Mr. Johnson's (William Stanford Davis) weird. But we just didn't know how much.

Frank ends up sleeping in the trap wrapped in the pelts after eating the seasoned compost. This matchup brought together two Philly casts: “Abbott Elementary” and “It’s Always Sunny in ...