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Pixel Art refers to the charming, simplistic, retro/renaissance style of very-low-resolution graphics, such as from the 1977-1995 Atari, GameBoy, & Super Nintendo (SNES) eras.

Near infinitely replayable games that usually feature, random generation, perma-death, and brutal difficulty. 

Science-fiction. Commonly including things like aliens, advanced technology, and settings of outer space or distant planets.