usually not included in final list of levels of the game because of their limited replay value. Minigame A minigame (also spelled mini-game or mini game, sometimes called a subgame or microgame) is a short video game often contained within another video game, and sometimes in application software or on a display of any form of hardware. A minigame contains different gameplay elements than the main game, may be optional, and is often smaller or more simplistic than the game in which it is contained. Minigames are sometimes also offered separately for free to promote the main game. Some minigames can also be bonus stages or secret levels. They are distinguishable from levels in that a level is an environment bound to a set of mechanics and rules that all defines all other normal levels in a game, whereas a minigame can use different rules and playstyles but may not necessarily be set in a different environment. Hidden features Level designers sometimes make hidden rooms and areas that usually require more effort for the player to reach or to notice. These usually give some additional rewards, such as ammo or powerups. They serve to induce players to explore. Sometimes, they serve as easter eggs, containing messages such as the level designers' names or pictures, or political or humorous messages. One of the first games with a 3D engine to feature hidden features was Wolfenstein 3D, where certain walls could be pushed to reveal hidden passages. Sometimes, a whole level may be designed as a secret level. Bonus stage A bonus stage (also known as a bonus level or bonus round) is a special level within a video game designed to reward the player or players, and typically allows the player to collect extra points or power-ups. Bonus stage either have no enemies or hazards, or replace the normal penalties for being struck by enemies or hazards with simply being thrown out of the bonus stage. Many bonus stages need to be activated or discovered in some manner, or certain conditions must be satisfied to access them. Otherwise, they appear after the player has completed a certain number of regular stages. Level bugs There are many map bugs that level designers try to avoid, but sometimes go unnoticed for some time. A player might get stuck in map geometry with no way to escape or to die. A player might be