Mysterious Stranger

Mysterious Stranger is a Perk in Fallout, Fallout 2, Fallout: New Vegas, and Fallout 3.

Fallout and Fallout 2
When you select this perk, there is a chance (30 + (2x Luck))% that your character will gain a temporary ally, but only in random encounters.

Details depend on the player's level:
 * 9-14: 50 HP, Leather Armor. (52 HP if stranger is female)
 * 15-18: 70 HP, combat leather jacket.
 * 19-22: 90 HP, Metal Armor.
 * 23-26: 110 HP, Combat Armor.
 * 27-29: 130 HP, Power Armor.


 * 9-13: Hunting Rifle or FN FAL.
 * 14-19: Assault Rifle or Combat Shotgun.
 * 20-26: Laser rifle or H&K CAWS.
 * 27-29: H&K G11.

Bugs
The stranger with the Hunting Rifle actually spawns Shotgun Shells as ammo instead of .223 FMJ. As such, the stranger only has 10 shots (which are spawned inside the weapon).

Fallout 3
You've gained your own personal guardian angel... armed with a fully loaded .44 Magnum. The Mysterious Stranger wears a fedora and overcoat, like the protagonists of 1950s film noir. With this perk, the Mysterious Stranger will appear occasionally in V.A.T.S. mode to lend a hand, with deadly efficiency. His magnum deals exactly 9000 damage per shot and will kill any enemy in one hit, including Super Mutant Behemoths. Regardless, he will still empty six shots into a chosen target.

The Lawbringer, Contract Killer, or Grim Reaper's Sprint perks will not grant their benefits if the Stranger finishes your target because technically you did not make the kill. If you are a slaver, be aware that mezzing NPCs in V.A.T.S will sometimes make the Mysterious Stranger appear, resulting in the death of your victim.

Additional Dialogue

 * Having the Mysterious Stranger perk opens up a new line of dialogue ("Maybe, if we're lucky, a friend of mine will show up to help us.") with Somah when you first arrive aboard Mothership Zeta. This does not go over well with Somah, and has no real effects.

Bugs

 * A rare glitch might occur when the Stranger appears. If the Stranger appears behind the player character or even your possible Follower, he might actually murder all of you. This has happened to a few players on occasion, but is only most common in small confined spaces, such as a house in Megaton.
 * The game may randomly freeze after the appearance of the Stranger.
 * The Stranger can often fail to kill a character or creature if they are positioned unfavorably (i.e. in an attempt to assassinate an enemy he can easily fall off a bridge or cliff or get stuck outside a building - which usually results in him running around pointlessly for a while until V.A.T.S. ends).
 * During V.A.T.S., it isn't uncommon to hear the Mysterious Stranger music, even if he does not appear. This most likely happens at times when he would have appeared to finish off your enemy, but you killed the enemy instead.
 * If you are attacking a swimming enemy (Mirelurks, for example) and the Stranger appears, he will fall into the water with the enemy and will swim in place, unable to attack because he is in water.
 * Sometimes when the Mysterious Stranger appears, he doesn't shoot. He'll just stand there, leaving you helpless. Another variant causes the Stranger to reload his magnum for the duration of his attack. If it jams, he may not attack at all.
 * When you enter V.A.T.S. it will be the slow motion scene as usual, but for some reason you get stuck in it once you're done shooting. The enemies and your followers (if you have any) will keep fighting each other but you can't leave V.A.T.S.. This probably happens when the Mysterious Stranger is to appear, and for some reason he didn't.
 * While in the Operation: Anchorage simulation, the Mysterious Stranger will sometimes appear and then ragdoll, you will then receive a message that the Mysterious Stranger is unconscious. When V.A.T.S. ends, gameplay will resume as normal.
 * The Mysterious Stranger will bug and be stuck inside walls or even filing cabinets rarely if you are on a certain point of view and small rooms in V.A.T.S..
 * It is possible to injure the Mysterious Stranger by using weapons that deal area damage from grenades to large cannons such as the Tesla Cannon, Fat Man, or Experimental MIRV. It will just give captions such as "Mysterious Stranger right leg crippled" or "Mysterious Stranger is unconscious."

Fallout: New Vegas
It is heavily implied that the Mysterious Stranger is the father of the Lonesome Drifter. In speech the Drifter will state that his father was a "Mysterious" man and that he was a "stranger" to his own family. The word Mysterious appears right above Stranger in the dialogue box. The Drifter also carries a unique .44 Magnum that looks remarkably like the Mysterious Stranger's revolver, it also plays the guitar notes that you hear when the Mysterious Stranger shows up.