Street Fighter 2 popularized and pretty much set to stone what a tournament fighter game should be. Mortal Kombat came first, but its single-player progression was this weird "tower" with some gimmick fights thrown in, like you vs 2.

Thinking about it, I'd say Mortal Kombat popularized the "REALLY fucking cheap sub boss/final boss" that many other fighting games have (looking at you, SNK) - I mean, good luck getting close to Goro in the first place.

I wonder which korean mmo could be considered as the one that de facto popularized pay-to-win as an integral mechanic.

Diablo hands down popularized not only the action RPG genre, but also having enemies as loot mystery boxes. One lucky kill and you could get your hands on a really great piece of equipment. The amount of clones speaks for itself.

I think Gran Turismo popularized the "carreer mode" of racing games.

Crush the Castle inspired Angry Birds and several other games with the same catapult mechanic. Loved that flash game way before Angry Birds was put on the App Store.

Arma 2-3 have been responsible for at least 3 major multiplayer genres.

WASD + mouse aim in FPS. Wolf3d, Doom1 and Blakestone used the arrow keys, spacebar and Ctrl back in the day. The arrows were turn, not strafe too.

I reckon it was some friends of mine in the 90s in Box Hill, Melbourne, Victoria who were the first to use WASD/mouse aim. Share house above a shop at the end of a tram line.

Doom or Wolfenstein birthed 3d fps I'm p sure 😁

Dune II - basically the grandfather of every RTS game out there (and incidentally very, very different from Dune I): opposing forces, resource collection, tech tree, fog of war, et cetera. Or perhaps it was (not World of) Warcraft, it's been too long and memory gets fuzzy.

I'm not 100% sure if factorio was the first, but the devs at Wube certainly perfected the idea and now there's a whole market for the "factory game" genre.

Ocarina of Time is the mother of modern 3D gaming with Z-targeting.

Elite was the first game to utilize procedural generation, which has been extremely popular across multiple genres.

https://en.wikipedia.org/wiki/Elite_(video_game)

https://www.guinnessworldrecords.com/world-records/first-use-of-procedural-generation-in-a-video-game

While some might not consider it a game mechanic I certainly do, as gaming the proceduraly created levels is a core part of certain games, see mapping tactics in Diablo 2 for example as you use knowledge of procedural generation to reduce the time to find and kill bosses!

Oblivion popularized fucking DLC, holy fucking shit I hate DLC so fucking much I pirated any games that has DLC, I don't mind expansion but DLC can crash and burn in a pile of dogshit

Battlefield 1942 introduced rideable vehicles to the maps.

Halo introduced regenerating health.

Souls games. Popularized invasions.