Let’s forget about the Oops TPK, but let’s discuss about the time it ended-up greatly, no matter whether the party decided t sacrify their life to save the world (or simply their honour) or that horror game where the PC found-out too late that they’re hopeless and bound to die
Level 2 party vs a Smothering Rug. We each went up to it alone, at different times. The last player ran into a side room with no exit, and after a few moments of silence, opened the door to see if it was gone.
Queue the horror movie music.