Video games that require mental skill as well as, or instead of, dexterity and quick reflexes. The term includes both games such as Lemmings that involve solving a series of puzzles, and the Tetris subgenre in which, although nothing that fits the usual dictionary definition of "puzzle" is present, doing well at the game requires mental skill in working out the best way to manipulate pieces to attain a certain objective. A single round of a puzzle game may appear in a game of another genre, particularly Adventure, as an obstacle to the player. It can be broken down into these sub-genres: