POLYBIUS was an arcade cabinet in 1981 that was part of a government-run psychology experiment based in Beaverton, Oregon. Players suffered from a series of unpleasant side effects, including amnesia, insomnia, night terrors and hallucinations. These few publicly staged arcade machines were said to have been visited periodically by men in black for the purpose of data-mining the machines and analyzing these effects. Eventually, all of these Polybius arcade machines disappeared from the arcade market.

And now you can have its logo as a keychain.