An action game is a video game genre that emphasizes physical challenges, including hand–eye coordination and reaction-time. The genre includes a large variety of sub-genres, such as fighting games, beat 'em ups, shooter games and platform games. Multiplayer online battle arena and some real-time strategy games are also considered action games. In an action game, the player typically controls a character often in the form of a protagonist or avatar. This player character must navigate a level, collecting objects, avoiding obstacles, and battling enemies with their natural skills as well as weapons and other tools at their disposal. At the end of a level or group of levels, the player must often defeat a boss enemy that is more challenging and often a major antagonist in the game's story. Enemy attacks and obstacles deplete the player character's health and lives, and the player receives a game over when they run out of lives. Alternatively, the player gets to the end of the game by finishing a sequence of levels to complete a final goal, and see the credits. But some action games, such as early arcade games, are unbeatable and have an indefinite number of levels; with the player's only goal being to get as far as they can to maximize their score.