Deathshot

Deathshot, p.n. in an RPG, an annoying, dangerous, or otherwise harmful NPC who travels with the character party, whom the party can not kill nor get rid of, because the gamemaster considers the NPC to be "his" or "her" character. [EDE]
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Addendum: Deathshot was an NPC tag-along in an otherwise popular long-running AD&D game. He was fond of screwing over the players and killing innocent people, and the players couldn't kill or ditch him because the gamemaster loved the character. [EDE]