Information asymmetry: when people know things that others don't, and vice-versa. A concept that underpins some of the very best multiplayer experiences, and the foundation of Scotland Yard: The Hunt for Mr X. Set on a large map of London, a team of the noble rozzers have one objective - track down that elusive, tantalising Mr X before he escapes.
The exact size of each game varies, but it's usually four coppers chasing down the villain. Each location in London is joined by transport links, and players move to any connected location on their turn by taxi, bus or tube. Mr X can see the police, and they can't see him. But three times during the game, on the third, eighth and fifteenth turn, his current location is shown.
All that the police have to do is get onto a square occupied by Mr X while he's still there, which results in the arrest and a glowing front page headline. The starting positions are randomised, so the first couple of turns tend to see the police moving towards train or tube stations - after Mr X's location is shown on the third turn, they can then cover a large area of the map quickly to get nearby (taxis and bus rides tend to be much shorter). This preamble always tends to run in the same way, and it's then that the hunt for Mr X really begins.