The rules of any given tabletop game do not have to be limited to what is listed in the rulebook.
The rules of Monopoly are good and fun. But really, the auction rules are lame, Free Parking needs something to make it more exciting, and shouldn't you be able to travel on railroads you own?
Welcome to House Rules. Any rule that players add to or change in a standardized game is a house rule, named after the varying rules used in casinos (where you bet against "the house"). House Rules are, in a way, the Fan Fiction of Board Games and Tabletop RPGs.
The Game Master can inflict his House Rules on the gaming group whether they want him to or not. This can be a recipe for social disaster if done poorly, or a welcomed improvement. In fact, some table top games encourage House Rules, and offer advice for how to make them fit with the rest of the game. However, attempting to impose your rules on the rest of the world may get you labeled as a Scrub or as the Stop Having Fun Guy, depending on the tone you use. If there is any ambiguity in a house rule, particularly with how it stacks with other rules, a Rules Lawyer may try to take advantage.
House Rules are not the same as errata, which are released by the publisher and are used nearly everywhere that knows about them. Errata are small corrections, or updates that the developers made before the game was officially published, but after the game has gone to print and can't be altered, while 'house rules' often fall under the category of 'whatever's convenient', either for gameplay reasons or to fix a broken aspect of the game system. Deliberately ignoring the errata, however, would be an example of house rules. Sometimes they can end up canon when former players start making the game and include their own favorite house rules in the errata or in newer editions.
Please note that while House does, in fact, rule, this is entirely unrelated. Also is not directly related to (but may be used to tweak) a House System. Not to be confused with the book House Rules, which is about a murder trial involving an eighteen-year-old with Asperger's Syndrome, or with The Cider House Rules.
For the video game equivalents, see Self-Imposed Challenge (undertaken within the mechanics of the game) and Game Mod (altering those mechanics themselves). See Variant Chess for a fiction-based trope with narrative uses. Also see Calvinball, which may be a result of a liberal application of this trope.
Ironically, Seto adapted to this new rule almost perfectly, while Yugi managed to defeat Noah using a Deckmaster that was almost worthless. Noah, on the other hand, used a Deckmaster that was likely more powerful than any other; he had to cheat in order to defeat Kaiba, and could not defeat Yugi. In short, his plan to use this House Rule to prove he was superior to his rival failed miserably.
The special rules for Turbo Duels in Yu-Gi-Oh! 5Ds (which involve the "Speed World" Field Spell which prevents the use of all Spell Cards except "Speed Spells", where the number of "Speed Counters" you have determines how powerful a Spell Card you can use) can also be considered House Rules.
Most recently, in the ongoing Yu-Gi-Oh! ARC-V, there are Action Duels, which combine dueling with performing arts. The rules are complex, and a brief summary of what is known so far is found here.
The above mentioned Monopoly has a plethora of house rules that have been played, to the point where some people are surprised when you show them in the rulebook that, no, that rule is not part of the official rules, but this one most certainly is. Here's some of the most popular over the years.
Putting various fines (mainly taxes) which, by strict rules, would go to the bank in the center of the board and giving all the money to whoever just landed on "Free Parking" is very popular. It's not part of the general rules because, in the endgame, a random landing on Free Parking may prevent a poor player from going bankrupt for several more turns, extending the game when it is already starting to get tiresome.
This is actually a rule in Monopoly Junior (set at a funfair), where Free Parking becomes "Uncle Pennybags' Loose Change," and the money comes from a couple of rides and the restrooms.
Likewise, many players are unaware that once all the houses and/or hotels are on the board, you can't just keep on buying more and marking their spot with pennies; once they're gone, they're gone unless someone decides to sell them. Many players who are aware of this make a House Rule allowing you to do the latter as a misguided attempt at an Anti-Frustration Feature, but it just make the game more frustrating, especially in combination with the above rule, as the same few players trade around the same couple thousand dollars with no end in sight, turning the endgame into an interminable Luck-Based Mission.
"Double Money for Landing on GO". Some sticklers will argue that it doesn't apply to cards that say "Go directly to GO" because they state specifically "Collect 200 dollars". Opposing sticklers will argue saying that they should get the 400 in addition to the extra 200 because it doesn't directly state the 200 dollars come from GO. This is how friendships are destroyed, families are broken and lives are lost.
Another fun house rule: Official Monopoly rules require any purchasable property that is not immediately purchased by the person who landed on it to be auctioned. A house rule is to leave such a property unowned (and not charging rent) until someone who is ready to purchase it lands on it. This rule can allow more expensive properties to go unowned until near the endgame.
This rule normally exists because either people can't be arsed with auctions, or there will be one wag who sets a new world record for the fastest person to say "OnepoundgoingoncegoingtwiceSOLDMINE".
More serious gamers, who usually turn their noses up at Monopoly, might find it more interesting with the inverse rule: any unowned property that is landed on immediately goes to auction, i.e., the person who landed on it does not get the option to buy it at face value first.
Referenced by Victoria Wood in a monologue about spending Christmas with a friend's family. Never play Monopoly with people who've been playing it together for decades, because everything you do will be wrong.
"No buying property on the first lap" is another very common one, intended to balance out the advantage gained by going first. Bad luck with the "Go To Jail" square can completely break this game, though.
The ability to merge into alliances and trusts is a very common house rule.
In what is probably a parody, the Screamsheet introduced Epic Monopoly, which adds bizarre random encounters including Nazis, Orson Welles, and streetwalkers to the game.
"No collecting rent while in jail" is an Obvious Rule Patch intended to prevent players from intentionally trying to go to jail and stay there for as long as possible in the endgame, when the risk of landing on another player's devastatingly built-up monopoly is far more significant than the chance of landing on one of the last two unowned properties, neither of which is of any strategic value.
In the Finnish classic board game Star of Africa it was possible to have a situation where nobody can win the game. After more than 50 years of various house rules to prevent this, a re-release finally fixed it.
The rules of Tigris & Euphrates say that in an external red conflict, temples with leaders next to them aren't removed. But really, isn't that a bit lame? The obvious alternative, however, that they're all removed, is simply too powerful. One compromise is to remove as many temples as possible in such a way that each leader still has at least one temple next to him.
Mahjong, especially the Japanese variant, has many house rules. Common house rules include:
Yakuman stacking: A few very special hand types (known as yakuman) are automatically worth the Cap of 32,000 points (subject to the x1.5 multiplier if the player who is holding the dealer button wins, for 48,000 total). On the even rarer occasion that someone completes a hand which fulfills more than one yakuman condition, this rule allows them to win 32,000 points per yakuman condition the hand fulfills. This makes it possible, albeit extremely improbable (the odds are better of winning the lottery twice in the same month), to form a hand worth 336,000 points.
Wareme: When someone wins a hand, whoever is sitting behind the broken tile wall (i.e. the wall where the initial draw started) wins and loses double.
Doukasen: When someone wins a hand, whoever is sitting behind the tile wall the last tile was drawn from wins and loses double.
Open Riichi: Upon declaration of Riichi, a player can reveal his/her entire hand (or just the portion that's relevant to what he/she needs as the last tile to win), so that opponents can figure out what he/she needs to win and avoid discarding those tile(s). 1 extra han (hand point) for winning the hand after doing so. An additional house sub-rule can make it worth a yakuman (the Cap of 13 han, converts to 32,000 Scoring Points) if the Open Riichi player gets the last tile from someone else's discard, and the losing player could have legally discarded a different tile that wouldn't have let the winner win from his/her discard.
Kuitan Nashi: The Tanyao yaku only counts if the hand is closed (formed without called discards). This is an Obvious Rule Patch to prevent players from calling tiles left and right to try and finish their hand with Tanyao to fulfill the 1-yaku requirement just to claim bonus points for dora.
Aotenjou ("Skyrocketing"): The exponential score formula that's normally used for hands worth less than 8,000 points is used for all hands, without the 8,000-point soft Cap. This means, for example, that a hand with 13 or more han is worth over 2 million points at a bare minimum, instead of the usual 32,000 hard cap.
Usually there is also a separate rule on how to handle yakuman (see "Yakuman stacking" above). In the Touhou fangame Touhou Unreal Mahjong, the Aotenjou mode yakuman rule is "yakuman are worth 13 han, and multiple yakuman stack multiplicatively", with a hard cap at 4 billion points.
The latest installment of the Mahjong Fight Club arcade series also adds a mode which uses one of several creative house rules (with which house rule being used rotating depending on the date). Some of the house rules include:
Each player can see the entire hand of the player on his/her left.
Each player can see what he/she will draw on his/her next turn assuming nobody takes another player's discard (which shifts the order).
Each player's starting hand is visible to everyone and those tiles remain visible for the hand; only drawn tiles are concealed.
Each player starts with only 13,000 points, making it much easier to bankrupt a player. Busting another player yields a bonus, deducted from the busted player(s).
Each player is timed on how long he/she takes for each turn. At the end of the match, if the player with the highest score has the fastest average time, they get a bonus, deducted from the player with the slowest average time.
The game One Thousand Blank White Cards is almost nothing but house rules; it's part of what makes it fun. To clarify, it's played like this: each player receives a hand of completely blank cards (five or seven, usually). At any time, a player may take a blank card and write its rules on it (along with drawing a picture of stick figures). Once a card has been written on, it can be played, and the rules written on it take effect. The house rule "no cards that allow one player to win instantly" is usually declared up front.
Once upon a time, house rules were the only way to have a M:tG game with more than two people. Also, rules taken for granted today like the limit of 4 of each card and "play or draw" (the choice between going first or being able to draw an extra card) started as house rules.
Magic: The Gathering can be quite interesting with or without a "draw seven when you run out of cards" rule — the two require vastly different strategies, of course, since such a rule can make emptying your hand a good thing and make cards that return to your hand a severe disadvantage.
One particular unofficial multiplayer format that evolved for Magic is the Five Colour Format, which has massive 200 (or 500) -card decks that require all 5 colours to have at least a minor presence in the deck.
One way to create a new variant is to add "Alara" to an old variant. In the Alara variant, you can have one color and its two allies, and the other Commander rules apply as well. This bans all four-color and five-color cards, including cards like the Skyship Weatherlight (for costing one mana of each color to activate), and any color that requires mana of one color and both its enemies.
A particularly popular House Rules format, Elder Dragon Highlander, has its own official unofficial rules put together by people outside of Wizards of the Coast.
And now it's been renamed Commander and been given a multiplayer set themed around it, while still not being an official WotC format.
A multi-player "Wargames" variant exists, named and themed after an old WCW event. Play begins after the participants choose lots and are seated in order, first to last, with turns proceeding in order. For the first interval, typically two or three rounds, only players one and two may attack or affect one another, while later players and their cards/hands/creatures/etc cannot be targeted, nor can players "not in play" affect other players, in play or otherwise, in any way.. After the first interval has passed, player #3 becomes a valid target and may himself begin to target others. Intervals proceed until all players are in play, and only after all players are in play can players be eliminated from the game. Before that point, players can have empty libraries or a life total of zero and still be in play until the last player joins, but once he does and he is in a losing condition, he or she is eliminated immediately. The rules are easily modifiable for team play, with all odd- and even-numbers players competing on the same side and randomly determining who gets the numerical advantage as the intervals progress. Obviously, these variants are heavily based around luck of the draw, as later players in large games have a huge advantage in building up lands and armies without interference until he or she is put in play, though instants and other targeting spells have a large chance of being discarded, since as the players not in play cannot target others, these spells can go to waste due to discarding due to hand limits. A common house rule to make things easier on early entrants is allowing players to reshuffle their graveyard back into their library once their library is empty, eliminating the empty library loss condition.
An additional variant, sometimes termed "Royal Rumble", is also played, with the only change being that players can be eliminated before all players are in play. Or even that there is a maximum number of players in play at any given time, with the next player in line being put in play once an existing player is eliminated.
The card game Hex Hex specifically states that whoever wins the game gets to make up a house rule which applies for the rest of the session. Popular ones include not being allowed to say the word "hex" and swapping the definitions of left and right.
Uno's house rules have gotten to the point that in many minds they have displaced the real rules. In the original, you cannot stack Draw Two/Draw Four cards, you play for score (number cards are worth their number; Skip, Reverse, and Draw Two are all worth 20, and Wilds are worth 50), with the lowest score winning once someone hits 500 points, and you can challenge Wild Draw Four cards (you're not supposed to play them if you have the color of the card on top of the pile; the loser of any challenge has to draw eight as a penalty). Most people don't play with these rules, to the extent that they won't even announce which house rule sets they play with when the game begins.
Those who do know the original rules, though, will sometimes use this to their advantage - particularly if "stacking" is called but removing the limitation on Draw Fours is not. More than one person with an incomplete grasp of the Uno rules has been challenged on their Draw Four play in a stacking sequence, gotten a quick refresher of the rules, and acquired a new Rival after being crushed with a Draw Thirty-Two.
Apples To Apples has several popular house rule addendums, including that everyone gets to submit one red card, and that once per game a judge can swap green cards during the judging phase without warning anyone.
There are certain card games that are entirely based on house rules. For example, one game called Mao has only one real rule at the start; it's exactly like Uno with regular playing cards (no draw cards or wildcards), and the winner of a hand can make up a rule each turn so long as it doesn't favor anybody in particular. It generally starts with at least one or two extra rules so that you can trip people up. An even more crazy version of this was a game where you could make a rule any time you played an 8 card, and the rule could do anything besides make you win instantly without playing a card.
An interesting variant is where you don't have to tell anyone what the new rule you just made up is. You can merely indicate that they have broken a rule when they do so. This, as the Illuminati example mentioned above, is best played with people you trust or that you'll never see again. Alternatively, the person making the rule up tells one other player, which rotates through the players with each new rule.
It's worth noting that it's illegal to talk about the rules of Mao. If you do, your punishment can range from card penalties to a permanent ban (a ban being for explaining the majority of the rules to someone who does not know how to play). You can also not alter the base rules of Mao (plural, there are more than one in every game I've played). The official statement is "The only rule I can tell you is this one."
A simpler variant of Mao has one person making a rule (which can be as perversely complicated as they like) about which cards can be played on which other cards, and not telling anyone what it is. Then, everyone else takes turns putting down cards. If their card doesn't fit the pattern, they have to take it back and lose their turn.
Nomic and similar games consist of nothing but house rules; that is, in fact, the point - they're an entire class of games where the point is that the rules are altered continuously throughout the game. Needless to say, these games tend to get far more complicated than mere humans can cope with. Several have been running continuously since 1993.
Fluxx already has card types that add rules and goals to the game. You can buy Fluxx Blanxx to get the same cards with no text on them.
From the publisher of Fluxx comes Icehouse, a bunch of plastic pyramids that can be put on their sides to indicate facing. Then they started publishing game after game that used those pieces. House rules ensued.
Crazy Eights. Oh, Crazy Eights. The basic rules are a discard while following suit or value. This is the only thing that people can agree upon. The following are but a small example of the house rules one may come across.
Eights: Usually wild. Sometimes, they change the suit to their own suit. Sometimes, the player gets to choose the suit they become. Other variants have it as skip a player.
Twos: Pick up two. Stacking them usually means the next person picks up 4, then 6, then 8.
Jacks: Skip a turn or reverse the rotation of players.
Aces: "Drop the bomb." This allows you to play every other card of that suit on top of your ace.
Queens: Pick up four. Stacking them might be additive, like with twos. Sometimes, you can add the twos to the run. Sometimes, only the Queen of Spades means picking up, and it usually means pick up 5. May or may not stack.
Sixes: "Silent Six". Talking results in gaining two cards.
King Of Hearts/Five Of Hearts: Dropping the King results in the next player taking five cards, unless they counter with the Five. If this happens, the player who used the King has to take ten cards.
Multiples. Do you have -tuples of the same value? Why not play them all at once!
Knock to declare your last card.
And that doesn't even begin to cover Crazy Eights variants, like Crazy Eight Countdown.
Similar is Last Card. The usual rules are Ace is wild, 2 is pick up two, 5 is pick up five and 10 skip a turn. Optional rules include Jack is reverse, 7 'blocks' a 2 or 5, or bounces it back to person who put it down. Sometimes pick up cards can be passed on by the recipient by stacking another one on top to add the effect, regardless of whether it is the same number as the original pick up. There can be disagreements over whether someone's win was legitimate if they didn't call 'Last card' one turn, then emptied their hand next turn by putting down several cards of the same number.
Being a game with countless "official" variations and even more unofficial ones, Poker is replete with house rules. Some popular ones:
Chase The Hammer: Only used in Texas Hold 'Em games, you win a small number of chips from every player if you win a hand having been dealt a seven and a deuce of different suits, the worst possible hand you can be dealt and nicknamed The Hammer.
"No check-raising" was a popular one for a while, but it's currently out of favor for making the game (especially limit games) more mechanical.
Bad beat jackpots: Players who suffer particularly bad beats are given a large consolation prize, often larger than the value of the hand itself. Common in casinos.
In home games, it's becoming popular to give each player one "Show Me" chip at the beginning of the night, which can be used once after a hand is completed to force a player to show whether they were bluffing or not.
The straddle bet: If you're sitting under the gun (i.e. to the left of the big blind, where you normally have to act first), you may place a bet equal to double the big blind before looking at your cards. This essentially turns you into the new big blind position (i.e. you get to act last in the first betting round) while simultaneously doubling the stakes for the first betting round. Some variations of the straddle bet rule allow the player to the left of a straddle bet to re-straddle for double the straddle bet, and some allow this doubling to continue until the player to left of the last (re-)straddle bet doesn't have enough money to re-double.
In Chrononauts, a purely-for-flavor house rule is that whenever you change a linchpin, you have to explain how you're changing it. If someone changes it back, they need to explain how they changed what you did. This can lead to some very amusing chains of events.
Hitler was killed by an orbital laser cannon. Then he wasn't, because Bob stole the power source. Then he was, because that was a decoy power source. Then....
Also very often in the most popular German card game, Skat. Many of these help to drive the score Serial Escalation (and note that Skat is often played for money, albeit not that much, depending on the score).
How Blinds (bidding X books before the cards are dealt) are supposed to work in Spades, or even if said gambit is available. Whether you can call for one anytime or only after you're down X points. Do you automatically get them if you go into negative points? Standard scoring for failed blind or double-points? How they work usually depends on who you play with.
The faux-gameMornington Crescent consists almost entirely of the players "arguing" about which house rules are in effect for the particular game. Minutiae such as what day of the week it is, whether the House of Lords is in session at the time of play, and how many buttons are on the shirt being worn by the player to your right can all potentially be of significance.
In addition to rules that apply to all its ballparks, Major League Baseball has a list of ground rules which apply to specific ballparks, as the shape and design of the field of play vary considerably between them (most notably the outfield fences, sometimes supporting infrastructure like catwalks as well). For example, the outfield walls of Wrigley Field (home of the Chicago Cubs) are covered in ivy, so special rules are in place that only apply to Wrigley Field (namely, if a batted ball gets lodged within the ivy and is no longer visible, play is dead when the fielder stops looking for it and all runner are awarded two bases). At present, of the 30 ballparks in MLB only three do not have ground rules beyond the universal ones that apply to all fields.
Tabletop RPGs are particularly prone to House Rules, as players introduced to a new system import their favorite rules from other RPGs.
Wargames suffer from this a lot. Munchkins often come up with new and unusual house rules to "improve" the game or to settle some "obvious imbalance". In reality, no house rules of this sort were ever good; house rules are supposed to be things like "My hill with trees counts as a hill and a forest" or "The bunker is sealed and indestructible, it's just impassable." House rules should not be "All Eldar always strike first because they are cool".
The tiers for this seem to go "More Fun> More Fair> More Realistic> Fluffier".
Rifts, in particular, is often modified. It's intentionally created with no balance to speak of, and each power, spell, and piece of technology is written without considering how it interacts with the rest of the system. Most of the rules were initially created for other Palladium games that focused on human (or human-ish) characters: Ninjas & Superspies, Teenage Mutant Ninja Turtles, Robotech, etc. Since Rifts has everything from super-powered humans to giant mecha to demons to gods in it, there aren't any guidelines for, say, when your martial arts stop being effective. (6-foot human throwing a 7-foot insect with Judo? Not mentioned, but probably okay. 6-foot human throwing a 25-foot demon? Still not mentioned.) For bonus points, the rules are (intentionally?) just slightly vague. For extra special bonus points, the entire Palladium game system (of which Rifts is a member) is supposedly cross-compatible, but each particular game uses slightly different rules. House Rules to the rescue!
Its gotten so bad that the creator of Rifts uses house rules in his own campaign. Frustratingly, he refuses to put them in an update supplement, even as optional rules.
Virtually all Pen and Paper roleplaying games have houserules of some kind, and in fact many games encourage a DM to alter or change rules to make for a smoother game.
'You are not playing White Wolf's Exalted, you are playing your ST's Exalted.'
One common such rule is 'no takebacks'. Once an action is declared, it is to be taken. This is generally implemented to stop players from endlessly changing their actions based on other people's actions. Intriguingly enough, White Wolf's World of Darkness (pre-reboot at least) contained an actual mechanic for changing one's action in the combat round.
GURPS suggests 'no takebacks' as an actual rule, with the caveat that if the player regrets their decision on a time frame that would have been fast enough in game, they can undo their action. The example they give is burning a document. If you shout "Wait!" within a few seconds, your character can probably salvage the document. If your character was using a flamethrower on the other hand...
GURPS suggests various possible house rules in the sourcebooks. Apparently the most popular house (that isn't suggested) is to separate the extremely broad IQ stat from also raising Perception and Will.
That got suggested in Compendium I, before the shift to the newest edition.
And one that became basically Ascended Fanon was the change to hit and fatigue points. Formerly, fatigue points (tiredness) was based on Strength, while hit points (being cut to pieces-ness) was based on Health. Compendium I suggested reversing them; after all, muscles can help stop injury, while someone who's fit should have more endurance in a marathon, right? As of 4th edition, that's official. (Also helps mages from trying to get 12 ST to help get the FP needed for their magic..)
Another notable line in GURPS: if a spellcasting roll critically fails, "the GM is free to impose any backfire he finds amusing, so long as he doesn't actually kill the caster. If this sounds unfair, it is! Magic is fickle."
The Fantasy Trip has several combat rules listed as optional (such as crippling hits). House rules to reduce wizards' dependence on physical strength (so that all the wizards don't look like Arnold Schwarzenegger), or make combat less lethal (so characters don't die off like flies), are popular.
Actively condoned by the rulebooks of Warhammer 40,000, which generally operates by the idea that if you and your opponent agree to the house rule, why not?
The "snake eyes on a Leadership test means an automatic pass" rule was taken from 40K and absorbed into the Warhammer Fantasy house-rule pool so spectacularly that a) many people were convinced it was an actual rule and b) with the latest edition these people became right.
Warhammer 40,000 has got an expansive group of house rules floating around on the internet, including among other things rules for fighting battles set during the Horus Heresy, a fan-made 5th edition Inquisition Codex, rules for designing your own Special Characters, rules for designing Land Raider variants, and Apocalypse formations for large numbers of Exorcist tanks.
These days, Mordheim has been abandoned by GW, so a variety of sources have put together a series of campaigns and variant rules for taking the system out of the ruins of the titular city.
By far the most ambitious attempt is Waffle Edition 40K which is trying to re-balance the WHOLE GAME after 6th edition produced little of value while screwing up the balance even more. Progress has been slow though and a lot of people have given up on it.
In fact, what ended up in 3rd Edition that wasn't in 2nd?
Critical hits and misses. Critical hits in (A)D&D were house rule territory. A natural 20 might always hit regardless of the target's armor class, but that hit itself was still a perfectly normal one dealing standard damage with no additional effects by the rules as written. (Now, some magic items like wounding and vorpal weapons would have abilities going off on certain high to-hit rolls, but that was just part of their magic, not the overall combat rules.) Then in AD&D 2, critical hits became an "optional" rule in the book. Unfortunately, one of the suggested options for critical hits was that a natural 20 always hits and deals double damage, so anyone who could only be hit on a 20 effectively had half as many total hit points!
So "AD&D 2.5" (Player's Options) got two critical hits options, one of them being a reasonably detailed and unified way to use both Subsystem Damage and Hit Point systems. To handle really big critters (giants vs. zaratan sort of thing) "believably" it needed expansion of size categories, but its uniformity made this trivial.
"Confirming" critical hits. PO did it via victim's saving throw. D&D 3 did it via requiring a second attack roll — many players took the opportunity to house rule that part out since it slowed down play.
A number of late-run 3.0 books were designed to be easily adapted to 3.5, but still require certain degrees of interpretation.
The 3.5 book Unearthed Arcana was nothing but a collection of common house rules as official variant rules. Since it was released under the OGL license it's available as part of the SRD online.
Natural 1s and 20s are very frequent house rule targets across the board. Many DMs consider them automatic success/failure on almost any sort of roll, and sometimes add additional effects to be rolled on a natural 20. By default, the only normal rolls affected in any special way by a natural 1 or 20 are attack rolls and saves. One solution made a better use of the "exploding dice" probability regression mechanics AD&D2 had for firearms. Another used extra condition "and beat the target number by X", used in PO.
The 3.x Diplomacy rules are particularly conspicuous, as, by the book, a focused character can persuade a horde of bloodthirsty enemies he does not share a language with to "take risks to aid" him in approximately six seconds. Unfortunately, some common house rules result in things like noblemen refusing to accept taxes from peasants because the deal of "I give you money for nothing" isn't rewarding enough to overcome the level difference.
Probably one of the most popular house rules in the third edition is adding experience points after each accomplishment (eg. defeating a monster) instead of at the end of each adventure (as suggested in Player's Handbook). Obviously the limit of one level-up per adventure is usually omitted as well.
The complete inverse is popular, too: ignore all of the math around tracking experience points, and everyone levels up when the GM says so. Removing that bit of accounting saves sanity for both GMs and players.
Lots of house rules, in fact, revolve around ignoring unwieldy rules or not tracking cumbersome equipment.
Original D&D was so convoluted it required much interpretation. Effectively each different interpretation was a house rule. It also expected that you'd have a copy of an earlier game Chainmail and a game from another company, Outdoor Survival. While the Dungeons & Dragons Rules Cyclopedia got all necessary rules within one roof, there were still a few things left undefined but either mentioned in other rulebooks or implied as knowledge in some other random rule. (e.g. Does drawing a weapon require 10 seconds, or does it cause you to lose initiative?)
Many groups also implement more generous ability score generation methods than the defaults listed in the book or allow rerolls when a character is stuck with nigh unplayable stats. This was more common in earlier editions when Honest Rolls Character was the default (six ability scores rolled in order with no rerolls). With third edition, the rules were changed to favor above average rolls (since the main characters are heroes) and to allow a complete set of rolls to be thrown out if they didn't meet certain minimum criteria. Point buy is also an official rule variant. So now, the Honest Rolls Character is a house rule.
Paranoia is particularly suited for house rules as the players are not supposed to know the rules and the GM is encouraged to remove, add or change the game any way they see fit. The GM can even change things as the game is progressing and the players are supposed to praise the decision.
Then again, half the time Paranoia is played without any rules as the GM pulls shit out of his ass, rolls dice behind a screen, and pretends to consult charts that don't exist. Typically this is for the best.
Players knowing the rules is treason.
ICE's Rolemaster system is designed to be very flexible and encourages the use of house rules.
Mutants & Masterminds is built on this trope. In a game where it's very easy (and surprisingly affordable) to get infinite attacks in a round, the core rule book spends a great deal of time letting the GM know that they have every right to disallow certain 'legal' actions. It's also not uncommon for certain rules to be ignored if they'll slow down the game.
House Rules for most Hero System campaigns were more about the flavor of the setting than modifying the actual game, though there were always additions to the already long list of Advantages and Disadvantages.
Big Eyes, Small Mouth, having been built with the entire anime genre in mind, requires House Rules and various GM fiats to keep the vaguely-written, easily exploitable phrasing on the book rules in check. While most of them are internally consistent, conflicts between opposing Attributes can very quickly devolve into shouting matches.
Spirit Of The Century despite being the first FATE game to hit the market had a notoriously bad stress system that was almost universally house ruled over. There are still a great many variations out there.
When Dresden Files came out it used one of these variations to have consequences be conditional, but mostly left things the same save for decreasing just how much stress characters could take. Well, without getting into Toughness Powers.
To wit, pretty much any incarnation of the Fate system post-SotC handled stress differently from it, and not all of them even did it the same way — Evil Hat's own The Dresden Files shortened the stress track as above, Crucible 7's licensed twins Starblazer Adventures and Legends Of Anglerre kept the length but turned the tracks strictly linear so that each point of damage would take off a box...
In addition, pretty much every incarnation of the Fate system invites players and Game Masters to create their own stunts as needed, though earlier versions with their extensive stunt shopping lists could make this task look rather daunting. The Fate Core System released in 2013 explicitly puts the responsibility of customizing the system to their own needs more into each playing group's own hands — tweaking the skill list to taste, creating new stunts and other add-on "extras", it's all on the table, usually complete with guidelines, explanations, and examples.
Exalted second edition has had many rules issues that led to everything from minor tweaks to massive mechanical rewrites to get rid of the problems. For example, some groups issue XP at character creation instead of the normal point-buy or hand out bonus points instead of XP, since the character creation system has flat costs for attributes and abilities while XP-based advancement has each dot cost progressively more, leading to people who failed to optimise being left in the dust due to the higher cost of reaching the same levels as their more min-maxed peers. Others have engaged in enormous projects to rewrite the more catastrophically broken material, such as most of Scroll ofthe Monk.
A pretty common feature in most multiplayer games is to include options in multiplayer game configuration screens is to remove specific elements, be they maps or items, from play, either for challenge reasons or because they were seen as annoying gamebreakers in a PvP situation.
Players of most MMORPGs tend to forbid using health potions during PVP as they immediately turn a skill and/or gear contest into a war of stock attrition.
People often impose restrictions on the battle system when doing battling in the Pokémon games, often based on popular tournament formats. Pokémon Battle Revolution even allows you to hardwire in these restrictions before the match begins.
Real-Time Strategy multi-player games often have an agreed "5 minutes no rush" rule, if the game doesn't support it itself.
Is sometimes taken to extremes. In Age of Empires, No Rush agreements can stretch as high as 45 minutes, even though the game includes the ability to start with extra resources or later in the tech tree specifically to avoid this issue.
Age of Empires III actually made this official with the "Treaty Mode", which prevents all combat until a time limit is reached.
It can even go further, some games have common rules amounting to "no subterranean/airborne/warping units can be used until you pass a "gate" or other arbitrary barrier around the enemy base" with ground units. Such rules are designed to prevent base building being a race to build said rapid-transport units to bring in engineers/monks/converters/other capturing units before the enemy can build effective defenses. While it's a noble intent, the rules can be so specific as to be annoying, and often unbalance games where one faction relies on traditional firepower and the other faction relies on stealth/trickery/speed/etc.
Most if not all electronic versions of Monopoly have selectable house rules built-in.
This was also the beginning of Griffball, as well as numerous other games in the Action Sack playlist.
In Star Wars Battlefront II, assault on Mos Eisley has these unofficial rules: 1) The arena is for dueling, 2) Interfering in a duel is a bannable offense, 3) Ayla Secura is cheap, 4) No Yoda either.
The Ur-Quan Masters (Star Control II) has a few for online games, mostly because the game itself doesn't enforce any standards:
Both players are limited to a number of "points" (which indicate how strong each ship is), usually 200.
Players pick their teams before connecting. No peeking at the other player's selection.
No more than one of any given ship is allowed. Without this rule, one player would be able to get a huge advantage by having multiple copies of tough-to-counter ships, like the Chmmr and Kohr-Ah. A variation is to allow duplicates, but only for ships that are worth less than 30 points (the largest number of points any ship has in the game).
Thraddash is banned. The main reason, other than it being a Game Breaker, is the way to use it properly drags out games way too much (staying away from the opponent with the afterburner while slowly draining the other ship's crew with the peashooter).
If a stalemate happens, whoever controls the fastest ship at the time is responsible for breaking the stalemate.
Culdcept allows for players to set a large number of house rules in multiplayer mode, including banning or limiting certain cards in decks, just like a judging board for a physical card game would.
In many arcades, players often line up coins or markers on the cabinet to set up a queue, and whenever the current player's turn ends, they must get off the machine so that the player whose marker is at the front of the queue goes next. This is usually the case for Rhythm Games, Fighting Games, and Driving Games, but on Light Gun Games, Shoot Em Ups, and some other types of games, not so much.