Complex sentence: Some of these games implement instances, which create a temporary copy of the game world and its characters, reserved for a subset of players; this allows each subset the chance to experience that part of the game without any interference from uninvited guests.
Split into simpler sentences: Some of these games implement instances, which create a temporary copy of the game world and its characters, reserved for a subset of players. This allows each subset the chance to experience that part of the game without any interference from uninvited guests.