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 mummystands 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.
Another episode has Sam leaping into a TV actor who plays a doctor. He gets kidnapped by an insane dysfunctional couple whom the wife is a rabid fan that can't tell the difference between TV and real life. Sam was held prisoner against his will in an isolated house in a setting no different than Misery.
Stephen Colbert performed a sketch with Scott Bakula on The Late Show wherein he (in place of Al), tries to get Sam to prevent Trump from becoming president in the same episode. Even includes the costumes from the original episode, to boot! https://www.youtube.com/watch?v=R0ScMs6_I8s
The Evil Leapers, who jump into your body or the bodies of people around you to ruin your life. And we don't even know why.