Mysterious Stanger Visits?

Get the Mysterious Stranger perk once you level up enough. I forget what level you get it, though. I think 12 or so?

I always found this Perk to be a waste....

Yes Exactly.

You Get Mysterious Stranger Perk at level 10 if you choose it. But you must have luck of 6.

He only appears at random in V.A.T.S mode if you get the enemy health down enough.

Quote form the official game guide....

"If at the end of a V.A.T.S attack, your opponent has less than 150 points of health, there is a 10% chance that Mysterious Stranger will show up and finish him off"

well its just one of those extra perks used for fun. I decided to get the sandman kill perk and it can reeally come in handy sneaky. just a quick slit of the throat and their done.
ps. you dont need a knife

i dont know why but the first time is saw him appear and with that music it made me piss myself laughing