A gimmick is a term used to describe a niche style of gameplay or level design that may only be favorable to a subset of Doom players. Maps such as Doom II's MAP23: Barrels o' Fun, feature a gimmick where the purpose of the level revolves mostly around the player outrunning a chain of exploding barrels to get to various safe zones. Another example is MAP08: Tricks and Traps, which features various gimmicks that do not necessarily pay respects to the usual Doom gameplay a player may come to expect. Some levels and megawads are designed around gameplay gimmicks such as Cyberdreams and Archvile Jump; while others revolve around a gimmick in level designing, such as 10 sectors, Claustrophobia 1024, and 1 Monster Megawad.
Secret levels are also often gimmicky: E2M9: Fortress of Mystery relies on exploiting infighting, E3M9: Warrens make the player believe he is replaying through the first level again before transforming the entire map, MAP31: Wolfenstein and MAP32: Grosse are recreations of maps from Wolfenstein 3D, MAP32: Go 2 It turns MAP01: Entryway into a slaughterfest...