Every game is conducted like a scenario. When the Space Marines accomplish a task, like locating an item and making an escape, they emerge victorious. Usually by eliminating them all, the Genestealers triumph by preventing the Space Marines from accomplishing their objective. One special mechanism is that the Space Marines have a 3-minute time constraint, and even less if a sergeant is killed, but the Genestealers have no time limit at all. This increases the stress in the game for the Marine player by simulating how much faster Genestealers move.