Part of the undeniable charm of "It's Always Sunny in Philadelphia," even after 20 years on television, lies in its whimsical soundtrack -- the satisfying irony of hearing rather pleasant tunes while watching the worst group of people wreak havoc across the city.

Die hard fans know that some of the best "Always Sunny" music comes from the show's originals, whether it's the legendary "The Nightman Cometh" musical or Charlie (Charlie Day)'s unexpectedly endearing "I Like Paddy's Pub."

But the soundtrack, composed of mostly free-to-use tunes, is the show's special sauce, from cheery transitions to the series-defining theme song, titled (almost unbelievably) "Temptation Sensation."

The bright waltz from German composer Heinz Kiessling has become synonymous with "Always Sunny," and Philadelphia as a whole: The Giants once notoriously played the track to troll the Eagles after a loss at MetLife Stadium in 2021, a move that would've enraged the Birds-loving "Sunny" gang. It's become so popular that one bride used it to walk down the aisle.