Monday Mashup: This is Spinal Tap

Population: One: Monday Mashup #46: This Is Spinal Tap
Byrant returns with a Monday Mashup that takes on that movie cultural touchstone, This is Spinal Tap.

A long slide to mediocrity, without even knowing that things are falling apart around you. The humor of cluelessness.
Maybe something like Buffy could work with this, with the players unknowingly under a curse as they go on a cross-country road trip, running into baddies as always happens, will it or no.
The opponents they are taking on get progressively weaker, but they are not immediately aware of it, because their powers have been sapped by the curse. Finally, it becomes far too obvious to the PCs that they have hit bottom, and then somehow have to extricate themselves from this predicament, perhaps hundreds of miles from home.