Fallout 4: Mysterious Stranger

Perk Usefulness and Mechanics

Fallout 4's Mysterious Stranger Perk is one that will raise many questions about its usefulness. How often does he appear, and is the Perk worth it? The Perk itself is a bit of a mystery, but some of the mechanics are known and explain why he doesn't appear as much as some would like. Here are the three ranks of this luck-based perk and what I know about it after testing:

Gameplay Effects & Utility
From analyzing game code, I could see that the Mysterious Stranger Perk will only fire at below 40% of a high-health opponent's life. It is possible he may appear sooner when the enemy has less than 150 HP. With this in mind, I got a deathclaw weakened and made a save that I would reload a couple dozen times and learned a few things by testing the Perk:

• Mysterious Stranger will only appear on the last shot in VATS. This means single shots (in and out of VATS) would make him appear more often.
• However, the chance the Stranger appears seems to be at around 20% for Rank 2. I can only assume it's half that at Rank 1, but can't confirm. I was not able to say that firing many shots will make it more likely he comes to finish the target on his last shot you make in VATS.
• Mysterious Stranger can miss with his shots, but it's likely the 95% accuracy cap or even his own accuracy. He can appear again if this happens. I have not seen the stranger fail to kill when his shot hits, however.
• He is capable of dealing 1,000 damage to an enemy and I've even seen a player report that he finished off a Mirelurk Queen for them.

That the Mysterious Stranger only appears when enemies are weakened (or just weak), along with the last shot mechanic, explains why plenty of people have called this a bad perk choice. It is going to come in handy later in the game or against challenging opponents more often than not. Considering that, I don't think it's bad at all but certainly no Rifleman or Gunslinger. You may want to use the fact that he only appears on the last shot of a VATS salvo to your advantage, though it may only be worthwhile in a pinch and when you're certain the enemy fulfills the requirement he appear. In a situation where you're low on AP and can only fire one shot, it may end the fight for you.

The chance the critical meter gets filled (which works with Critical Banker, giving you a full bar) seems to be 25% from reading the game code. It being tied to him appearing, which is already rare, means the first two ranks of this Perk are likely more useful than the final rank, though it does fit into a luck-heavy build.

For a luck-based build that relies on those Perks which synergize incredibly well- four leaf clover, grim reaper's sprint, better criticals and critical banker - this adds another means of filling the meter and a nice random kill for you - and you do get the XP. Against legendary opponents and enemies like Yao Guai and Deathclaws (maybe even Mirelurk Queens) the Mysterious Stranger can do some amazing damage and possibly even save your life once in a while. It's a Perk that is more entertaining than functional, but the Mysterious Stranger is a nice addition to your arsenal.