You've heard stories of a lone wander who at the most curious times helps those in combat he deems worthy. He vanishes just as suddenly as he appears, this mystery man is an unpredictable but powerful ally.
Every turn, at the start of your turn there is a 5% chance that a Pale Stranger (Pathfinder RPG - Bestiary 3) will appear and attack your opponents then disappear. At level 1 he makes a single attack at his highest attack roll. At level 7 he makes three attacks at +15, +10, and +5. At level 14 he makes his maximum amount of attacks.
Effects that would prevent conjuration magic prevent the Mysterious Stranger from appearing.