Puzzles may need to be solved before the player can progress to the next section of the game. Often it may not be clear to players exactly what the puzzle is, or whether the an in-game items needs to be attained before it is even possible to solve it.
If a person is made of metal and has circuitry instead of a circulatory system, then their game belongs on this list.
The proprietary game engine(s) used by the indie games designed using the RPG Maker series of game development software.
The Sanity Meter gives the player insight on exactly how close their character is to losing their mind. Doubled with strange effects when the meter is low, the Sanity Meter can really start messing with you.
An eight legged arachnid. Some make webs to catch prey and some are poisonous. None have made a web grand enough to be called a parlor, though.
Using stealth often requires the player to accomplish their objective without being detected by enemies. Methods of detection can vary from game to game, and can be based on an enemy's line of sight, how quiet the player is, or even how the player interacts with the environment.