Snap plague

snap plague, n. an imaginary disease that kills player characters instantly and without warning, and for which there is no defense, cure or treatment; see DMO. [GJ1]
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Addendum: From the same AD&D game that produced Deathshot. The DM warned players that if they misbehaved, their characters might fall prey to the snap plague (as in snap! you're dead!). [GJ1]