This is based on opinion. Please don't list it on a work's trope example list.
Nightmare Fuel / FreQuency
John's dream (as the timeline changes again), the audience is led to believe that it's a remnant memory of his father's funeral before the changes in the past. Then we find out it was his mother's funeral.
In a rather frightening case of What Might Have Been, Frank gets caught by Shepard (the Nightingale killer) while trying to protect the nurses and almost becomes a victim himself. It's only by the grace of two hippies interrupting Shepard that he was spared.
Shepard's hand getting shot off in the past and then necrotizing and withering away to nothing in the present.