Came into possession of a jigsaw puzzle that was cursed like the video in Ring. Anyone who finished it would supposedly die within fourteen days. We didn't believe it at first, so we decided to do it. The puzzle itself was huge, several yards across, with big wooden pieces. It was more like a model train landscape. It showed a seaside village with underwater caves beneath it.
As we finished more and more of the puzzle, weird things started to happen. One person was wiping the graffiti off the inside of a window, and someone else saw her reach up and erase her own face. There was another face underneath. Someone else was chased by something into the caves under the village. She saw the thing there; it was some kind of oddly-shaped skeleton with colored lights playing over it, which was then inhaled like smoke by a Venus-Flytrap-like mouth with sharp teeth. Just to be clear, the creature wasn't just the skeleton or the mouth, it was both in combination with each other and the act of one inhaling the other. It was implied that these were the creatures that had originally made the puzzle.
The puzzle was clever. It only showed its true self to people who were alone, and it only did it at certain times. When we started to realize that something strange was going on, the puzzle stopped doing anything for a while, so that we would assume that the people who had seen strange things were just imagining them. Eventually, we figured this out, and we knew that there was something bad happening; however, we knew we would finish the puzzle anyway, because we were the kind of people who couldn't not finish a jigsaw puzzle.