Beat 'em up (also known as brawler) is a video game genre featuring hand-to-hand combat between the protagonist and an improbably large number of opponents. These games typically take place in urban settings and feature crime-fighting and revenge-based plots, though some games may employ historical, sci-fi or fantasy themes. Traditional beat 'em ups take place in scrolling, two-dimensional (2D) levels, though some later games feature more open three-dimensional (3D) environments with yet larger numbers of enemies. These games are noted for their simple gameplay, a source of both critical acclaim and derision. Two-player cooperative gameplay and multiple player characters are also hallmarks of the genre.