Knife and Candle is a minigame, so to speak, in the browser game of Fallen London. It is an underground league of what basically equates to the game of Assassin, the live action game played with mock weapons as players try to be the last person standing. It is usually played on college campuses and other such small areas, but I have seen it played on larger areas. Think of it as a non-lethal version of the movie “The Tournament”, for example.
The reason I bring this up is it is an interesting idea that I think I might be incorporating into my tabletop games in some variation. It doesn’t have to be lethal, it could just be as simple as stealing a bandana from people or attacking them with stun weaponry in a Sci-fi campaign. The idea that sets this apart from any other random encounter is this is something the players can volunteer for and also can become active in themselves. You would have the random NPC chances of an encounter, but the players can also go looking for other people who take part in it.
The exactly system of how it would work is up to the GM. In the real world, eliminations might include hitting the target with an airsoft gun, striking them with a toy plastic lightsaber, or putting a dash of hot sauce (“poison”) in the target’s food, though others may be splashing them with water or even just taking their picture. In a game world, I can see it being the first to strike, perhaps using a magical weapon designed to do little to no damage but just count the hit.
You can have some kind of reward for the victor, perhaps something like a monetary prize and some sort of roleplay award like access to a special club or tutor from a key figure, such as the Avatar: The Last Airbender episode “Sokka’s Master”. It can also be as simple as a title or similar that only carries respect in certain circles but it would be quite useful if the players won it.
So, beyond rewards they might not normally have access to and access to people they wouldn’t, like the assassin’s guild agents. You could have NPCs come to them to help in their attacks, or even have plots being made to have the PCs get an NPC to a specific place, or the PCs bodyguarding someone and the NPC trying to sneak in for just a touch.