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Uses two-dimensional "sprites", 2D images created and used on a flat plane, as opposed to the three-dimensional models or environments found in 3D games.

Utilizing content created by algorithms rather than human made content. Often utilizes a "seed," a relatively small string that is used to control the randomization algorithm that generates the entire world.

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

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Unity is a game engine for 2D, 3D, AR and more