A role-playing game is a game in which players assume the roles of characters in a fictional setting. Players take responsibility for acting out these roles within a narrative, either through literal acting or through a process of structured decision-making or character development. Actions taken within many games succeed or fail according to a formal system of rules and guidelines. There are several forms of RPG. The original form, sometimes called the tabletop RPG, is conducted through discussion, whereas in live action role-playing games players physically perform their characters' actions. In both of these forms, an arranger called a game master usually decides on the rules and setting to be used and acts as referee, while each of the other players plays the role of a single character. Several varieties of RPG also exist in electronic media, such as multi-player text-based MUDs and their graphics-based successors, massively multiplayer online role-playing games. Role-playing games also include single-player offline role-playing video games in which players control a character or team who undertake quests, and may include capabilities that advance using statistical mechanics.