This is based on opinion. Please don't list it on a work's trope example list.
Nightmare Fuel / Quantum Leap
One particular episode revolves around a villain faking a mummy's curse to steal its treasures, revealing how he did it all in the end. Then said mummy stands up and strangles him while the survivors flee in terror. Sam leaps out before we find out how it ends.
It's even scarier because a wall separates them from the villain and the mummy. You don't see it happen; you only hear the screams. Al is able to pass through the wall to check it out, but immediately comes running back out, saying, "He's killing him."
There's also the episode where Sam leaps into a death row inmate with only days left before his execution. He's able to complete his mission just in time to leap out while being electrocuted in the electric chair.
To clarify, Sam leaps into a horror novelist from The '60s and, within just a few moments of arrival, a man falls to his death from a ladder, it having been moved by a goat, which seems to appear and disappearthroughout the episode, and Sam's the only one who can see it. As time passes, other characters get killed off in increasingly creepy ways - and to bring this Up to Eleven, something is writing the murders in Sam's host's typewriter seemingly as they occur. Then it turns out that the goat is actually Satan, who's essentially been trolling Sam throughout the episode and steadily wearing him down, before taking human form and nearly strangling Sam in an extremelyMind Screw-ish sequence. Thankfully, Sam Beckett Strangles Satan and resets the episode to the very beginning, but without the devil causing mayhem, nobody dies this time around. And then, it turns that the allusions to horror novels from Sam's own time period has effectively inspired their own creation, because the host's assistant was a young Stephen King.