In an action game, the player typically controls the avatar of a protagonist. The avatar must navigate a game level, collecting objects, avoiding obstacles, and battling enemies with various attacks. At the end of a level or group of levels, the player must often defeat a large boss enemy that is larger and more challenging than other enemies. Enemy attacks and obstacles deplete the avatar's health and lives, and the game is over when the player runs out of lives. Alternatively, the player wins the game by finishing a sequence of levels. But many action games are unbeatable and have an indefinite number of levels, and the player's only goal is to maximize their score by collecting objects and defeating enemies.