Surfing

I was researching a bit about surfing for an assignment that involved a collectables map - basically the player runs around and picks up stuff.  My map ended up being a 3rd person greyboxed semi-homage of Perfect Stride, where each thing you pick up makes you move faster.

I'm not super into the result, but in the process became fascinated by videos of "surf maps" - acrobatic user-created levels that take advantage of quirks in Source's physics engine.  In surfing, your avatar is essentially "falling" against a sharply-angled surface, and you prevent yourself from falling off by strafing in the direction of the bank.  Surf maps require precise control of both the surfing mechanic and the equally idiosyncratic air-strafing controls that allow you to steer in mid-air.

The design of these surf maps varies - a typical map is a straight PointA-to-PointB run, but some of the most impressive videos are spiraling death rooms that require retraversals and careful speed control.  Some designers integrate surfing into typical death match maps, making for frenetic rollerball-style gameplay.

Surfing isn't an official Source-sanctioned sport (as far as I know), but skiing in Tribes is a similar  FPS mod mechanic that managed to become cannon.  After Tribes developers noticed the ubiquitous use of skiing in the first game, they made the mod mechanic a part of the main game from the second entry on.  It's not a niche map typology like surfing is (skiing courses do exist, though), but a primary way of moving around the maps.

This phenomenon of idiosyncratic FPS movement mods seems to be a relic of the early 2000's.  Both Halo and GTA have modding communities built around making over-the-top race maps, but these are based on a core feature of the game, rather than a hackey emergent property of the physics engine.  2010's FPS design seemed much more concerned with "realism" than action, a trend that's beginning to reverse.  It'll be interesting to see if an idiosyncratic mechanism like surfing or skiing arises from, say, Titanfall 2's wall running and grappling hook.