An old arcade game from 1981 called Polybius caused children nightmares, amnesia, and in some versions of the myth, even suicide. It was made by a company called "Sinneslöschen", German for 'sense deletion'.
There is no evidence that this game ever existed beyond the urban legend and an inconsistent interview with a programmer who claimed to have worked on it. Some conspiracy theorists claim that the game was installed and removed by "Men In Black".
A game released around the name time, Tempest, was recalled and retooled after it became clear that it could cause vertigo, motion sickness, epileptic seizures and other adverse effects. Polybius is often compared to Tempest in retellings of the story.
The name is a reference to Polybius, a greek historian who asserted that historians ought not repeat anything that cannot be verified. This reference supports the idea that Polybius is a joke or hoax.