When a game is developed, its designers come up with some core gameplay mechanics. As players play these games, however, they come up with new strategies and ideas resulting from putting individual mechanics together.
This article (of necessity) will only list notable examples, such as ones that have been given names by players.
Compare Emergent Narrative. Unlike (but closely related to) Gameplay Derailment, emergent gameplay features are generally seen as positive developments. May result from Good Bad Bugs, but bugs are not necessary. Metagames of competitive games are examples of emergent gameplay. Sequence Breaking and speedrunning are also examples, as are Video Game Caring Potential and Video Game Cruelty Potential when not tied to the actual plot. The Immersive Sim genre puts emergent gameplay on the forefront of its game design.
- Metroid: The maze-like structure and open-endedness of the first game was very interesting to speedrunners, since it allowed them to devise and test alternative routes, intended or not, through the game. Its third installment, Super Metroid, continues to be a widely-appreciated game, with Good Bad Bugs still being discovered that allow new speed tricks. Furthermore, said openness helped give rise to the Metroidvania genre.
- Combos in Fighting Games started out as this. Players were never intended to be able string multiple attacks together in the original Street Fighter II, however once the players figured out how to do them, the developers acknowledged them, as did every other fighting game developer at the time. Even today, the majority of the combos in these games are things that the players themselves create. In fact, it's generally acknowledged that one of the marks of a good fighting game is how much freedom it provides the player in terms of developing combos.
- Super Smash Bros.:
- Released as a fun, random, chaotic party game, Super Smash Bros. 64 and Melee have garnered much competitive attention for their astonishing, completely accidental technical depth. This video doesn't even begin to explain.
- Super Smash Bros. Brawl was a conscious attempt to close the gaping chasm between skill levels in Melee, by slowing the overall pace and streamlining most high-level techniques out. Opinions on the matter are mixed; most competitive players will point out that Melee was still a perfectly functional party game for people who didn't care to learn to wavedash, and casual players openly appreciate a larger character roster, stage selection and item list. All the same, competitive play developed, a new metagame arose and the skill gap opened anew.
One of the major things they were trying to get rid of were a lot of so-called "technical skills" — that is to say, very difficult to execute in-game commands which require a lot of practice to perform. Mechanics like wavedashing (which more or less replaced normal movement in Super Smash Bros. Melee) and L-cancelling (which was simply a case of bad design — there's never any reason not to L-cancel every move ever, so why is it the game in the first place?) were deliberately removed in order to simplify the controls. They largely succeeded at that, but the more people practice a fighting game, the more emergent gameplay tends to come out.
- Nidhogg is based around a six button/key control scheme, with a very advanced set of actions, even when four of those buttons are directional buttons.
- Originally, Starsiege Tribes was a tactical FPS, based on vehicles, and teamwork with massive open maps that would be nigh-impossible to practically cross on foot. And then players discovered that by "Hopping" using their jetpacks, they could essentially disable friction for their character, letting them "Ski" down slopes at immense speeds, and use the built up momentum to hurl themselves across the map. Soon players were using client-side macros to automate skiing at the ideal rate, superseding vehicles as the favored form of transportation. By Tribes 2, skiing had become an official feature, and the game's largely projectile-based arsenal would lead to a game of speed, trajectory prediction, and reflexes, with the well-earned title of "World's fastest shooter".
- The idea for Left 4 Dead came about when Turtle Rock Studios (who developed L4D) were developing the bots for Counter-Strike: Condition Zero and decided to play game where there were a ton of bots, players versus bots, and the bots on very hard with knives only. The result is very similar to the Horde Zerg rushing at times in L4D.
- Online free-to-play shooter GunZ: The Duel began as a fairly standard shooter, albeit with wall-jumping and other feats of badassery. Then, the playerbase discovered a number of bugs; these days, it's difficult to compete if you aren't proficient in the styles of play known as K-style, D-Style, or E-Style.
- In Final Fantasy XI, the ninja job was introduced with the intention that players would use it as a damage dealer that would use magical ninjutsu to supplement physical damage. However, players discovered that the Utsusemi ninjutsu, which would nullify attacks for a few times, coupled with the ninja's great evasion stats, made it a great choice for a tank. Eventually, developers began producing gear for ninjas that complemented this play style instead.
- Nudging a pinball machine to save an otherwise doomed ball has become an allowed maneuver in competitions, as long as you don't tilt. The technique of banging the bottom of the table to knock the ball over a divider and back into play, on the other hand, remains universally banned.
- Starcraft: being able to tell where a (competitive) opponent's base is by how long it takes their scout to find you.
- Kerbal Space Program: Due to the game's Wide Open Sandbox nature and the diversity of available parts, quite a few people find ways to have fun with the game without launching rockets into space at all, or by finding unusual uses for game parts. Geofley's Cove, a fully aquatic base on Laythe note , is one of the less outlandish examples.
- Dwarf Fortress: By sheer weight of the amount of simulations such as weather, erosion, and population density (among other things), there is quite a bit of emergent gameplay. One of the most important concepts to know to create a running fortress in less than a few days of gameplay are pump stacks, which are clusters of pumps that allow for instant transportation of water or magma from any lower z-level to the top of the stack.
- In some installments of the Thief series:
- Players were able to figure out that throwing a wooden crate onto a ledge and then shooting a rope arrow into it was one way of being able to use rope arrows in a space that otherwise seemed unsuitable to them (as they can only stick into wood or soil). The Fan Sequel The Dark Mod actually notes and briefly touches upon utilising the crate-roping method in its tutorial mission.
- Then there are the occasional cases of players tricking various, mutually hostile NPCs into fighting each other.
- Starting in Dungeons & Dragons 3rd edition, the codifying of rules that were previously only the purview of the DM combined with the rise of the internet (and with it the ability to easily share information) led to optimization. Among the most well-known (and controversial) outcomes of this optimization were the tier system for classes in 3.5e, and the guide to being Batman in 3.5e, a wizard playstyle that eschews traditionally-popular spells like Fireball to instead prepare spells that buff party members, debuff enemies, control the battlefield, perform utility tasks, or instantly kill/render helpless enemies.
- Dominance in dragon breeding sim Flight Rising was intended as, essentially, a dragon sink—a way to reconcile the mechanics of having infinite dragons but finite lair space by allowing people to get rid of dragons permanently ("exalting" them to the player's flight's deity) in exchange for currency, with the three flights that exalt the most dragons relative to their active populations gaining minor in-game bonuses. To say that it worked is an understatement; players soon realized that they could intentionally exalt as many dragons as possible to gain dominance during a particular week, and thus dom pushes were born. Particularly intense conquest battles involve flights exalting thousands of dragons, player-organized events and raffles to encourage players of non-participating flights to give or sell dragons for the organizers' flight to exalt, and the winners spending so much treasure that they can't take advantage of the actual benefits of having dominance. It's such a big part of the game that a not-insignificant section of players either ignore the actual dragon breeding altogether or only breed dragons for the sole purpose of exalting them.
- Go Cross Campus: Spies (people signing up accounts on opposing teams), Special Forces (people who make their moves late in the turn so as to prevent spies from being effective), and Swaps ("trading" territories between allied teams to give both teams conquer bonuses).
- NationStates: The World Assembly Delegate election system gave birth to Raiding/Defending, where organizations compete to take over or protect regions by forcefully electing someone and using the delegacy's powers such as regional appearance or ejecting nations.
- Warlight: As a Risk-like online indie game, there is little context provided and hard rules are only combat-oriented, yet players have come up with diplomatic games and scenarios with made-up rules. Those tend to provide pretty good roleplay.
- The Hellevator (a vertical tunnel stretching from the surface down to Hell) and the Skybridge (a bridge in mid-air, used to traverse the upper part of the map and for quick horizontal travel).
- Also several methods to exploit Good Bad Bugs to generate more liquid (water, lava and honey) than what is normally available, otherwise known as the liquid tile duplication bug.
- The biggest and most versatile example is the "hoik", which is based on a sloped tile collision glitch and is used for a variety of purposes from ultra-fast transport and glitching through otherwise solid blocks to creating a functional computer and fully-automated boss killing machines in conjunction with the game's switch-and-wiring mechanics, which are highly versatile in themselves.
- Minecraft: The game as a whole has a lot of this, but one of the most notable examples is the redstone system of which a wide manner of contraptions have been made, including 16-bit computers.
- TerraTech's building system and physics engine allow for a lot of creativity. While an individual tech cannot have moving parts, players have built "multi-techs" such as walkers, tricycles and tanks with a separate tech for each wheel, leg or turret. These techs have varying degrees of practicality in the campaign.
- A notable example is the popular hover glitch. If a tech contains a hover plate facing a wheel, the plate generates continuous thrust in one direction, much like a fan blowing on a sail. It also allows the tech to use ground controls whilst airborne. Players have exploited the hover glitch to build airships and perpetual motion machines.