As a genre-wide example if you ever wonder why a tabletop game is seemingly over-wordy on their explanation and being very precise, even spelling out things that seem like common sense, you have the mentality behind this trope to thank for that.
Old time wargamers of the Avalon Hill type may remember the nightmarish nonsense — like losing all of the British Empire to an attack carried out on London by a single airborne unit — that followed trying to play Rise and Decline of the Third Reich in its first edition in the mid 1970s. (The game's designer, John Prados, is brilliant at concept, but, even in the seventh edition published in 2000, proved that he still can't write rules for doodly.....)
This trope is Mr. Welch's bread and butter, even if the GM doesn't tend to be cooperative. The phrase "even if the rules allow it" and variants thereof appear no less than 47 times throughout the ever-growing list.
in the Axis & Allies miniatures game, air units were a late addition, meaning a lot of previous cards weren't prepared for their entry. Thus, units that should not be able to attack planes, like mortars and certain assault guns, can. Worst of all, land mines can affect planes. Those are some epicallybouncing betties.
Errata dictates that units with the "bombardment" ability can no longer attack planes, eliminating most ground artillery from the equation, but mines and mortars are still okay.
The Lore of Blood Bowl is rife with coaches doing whatever it takes to win. For example, players are strictly forbidden from carrying weapons on the pitch. Where most players figured it didn't count as a weapon if the blades were fixed to the armour, the Dwarves argued it meant riding a bulldozer on the field was allowed - it's not carried, is it? The actual gameplay reflects that spirit. In first and second edition of the game, the rulebooks for the various ways a player could cheat were almost as long as the actual game's rules (and more byzantine).
The Blue Rose setting has an in-universe example. A minor landmark of Aldis is its Plinth, a sort of public pulpit atop which people give performances. Usually these performances are innocuous things like juggling or dancing or monologuing on a subject important to the performer, but nothing is forbidden atop the Plinth because Aldeans respect freedom of speech so much. This leads to problems when a heartbroken lover plans to kill herself there, as a way of protesting her Parental Marriage Veto. Of course, suicide on the Plinth would be banned after she succeeds (if the PCs don't manage to stop her), but that won't bring her life back...
Pledges in Changeling: The Lost practically beg the player to use this trope, which The Fair Folk love. There's no such thing as "the spirit of the agreement", and parties can be bound to a Pledge without understanding the terms or even knowing they're entering a contact. For example, the Hag of Henslowe Park infamously offers a year of good fortune in exchange for a year of enslavement — a fate that can be averted by thanking her for her aid, not that she tells people about that part.
Apparently, the official rules once had a loophole that rendered the game 1.e4 e5 2.Bc4 Nc6 3.Qxf7 mate a victory for Whitenote if you can't read Chess directions, this is a variation on the famous Scholar's Mate: White is cheating by moving his Queen in a direction other than a straight line. Although the White Queen cannot move this way legally, checkmate ended the game. The other side could only claim an illegal move while the game was still in play. After a checkmate, legal move or not, it was too late to penalize the cheater for cheating. Unsurprisingly, the rule was patched shortly after discovery to state that the checkmating move must be legal.
For a while, there was no rule that you couldn't promote a pawn into an enemy piece to block the other player's path.
There is a similar case of promoting a pawn into a king. (Some stories have this "loophole" as a misunderstanding of the rules by a newcomer, caused by an incomplete explanation by his opponent, and the newcomer insisting on following the rules as first explained.) Although technically, this makes it worse for the player, as the rule is that someone whose king has been checkmated has lost the game, so having two kings is just two ways to lose. (Although if you were very clever, you could combine this with the previous loophole and promote a pawn into an enemy king. Bonus points if it's in a position already in checkmate.)
Castling can be performed with a king and a rook which have never moved from the position they were placed. Which led to someone creating an Urban Legend of Zelda claiming that you could promote their king's pawn into a rook and using it to castle vertically, until the rules were rewritten to prevent this. In reality, the FIDE laws never allowed this.
Munchkins in Dungeons & Dragons are worse than Rules Lawyers: some players go for full-blown Loophole Abuse. The DM can, of course, veto any action you do or change the rules at any time with Rule Zero, but it is not necessary to mention this for every example (D&D players have a penchant for seeking out loopholes for fun, without ever expecting to get away with abusing them).
Perhaps the classic example was the 3.0 Edition "Bag O' Rats Fighter". This involved a Fighter using the Whirlwind Attack and Great Cleave feats while dumping a sack full of live rats at his feet to get an Attack of Opportunity for each of the rats he killed — gaining a dozen or more extra attacks against his opponent in a single combat round! While technically legal according to the rules as written, no sane and reasonable DM should allow it. In 3.5 Edition, it got an Obvious Rule Patch stating that when using Whirlwind Attack, the character wasn't allowed to make bonus attacks from other sources, like the Haste spell or Great Cleave feat.
It was long believed that players could theoretically turn Locate City into a nuclear bomb. This turns out to not actually work, for fiddly technical reasons, but by the time that was discovered, the theory had been developed well enough to be quickly applied to a different spell that lacked those problems.
Others recovered from infinite damage by drowning themselves. Taken literally, the drowning rules set your hit points to zero, even if they're negative. And then "It's Wet Outside" lets someone make a heal check to stop drowning.
Passing an item hand to hand is a free action (doesn't take up time), so if you line up a few thousand people you can get an object to travel miles in six seconds. Then the last person throws it. This is commonly called the "Peasant Railgun". note The end result is a regular thrown object, since Dungeons and Dragons only bases thrown-object damage on the strength of the thrower and size of the object.
You can also have one player stand on another player's shoulders and pick him up as a free action. Then the other player picks him up. Since this is all a free action, there is no time for them to fall, and thus they can fly by repeatedly picking each other up in midair.
If you have someone in a grapple, you can move them at a fraction of your normal movement speed, assuming they fail (or don't try) to resist. So if you have a half dozen people or so in a group hug and none of them resisting, they can travel faster than running speed. Get enough people and you can break the sound barrier.
Further, all characters in a grapple are in the same square. There's also a rule that up to three people can grapple with one target. With some creative planning on the part of the grapplers, you can get it so that the entire population of a planet is in one square, which is 5 feet in game terms. There's also a rule as to what happens when players break a grapple (each member of the grapple is shoved to the nearest empty square immediately). This can result in characters going faster than the speed of light in order to land on a properly empty square.
Dropping an item is a free action, as well. And if you happen to be fireproof and are standing next to an enemy while carrying, say, five hundred units of alchemist's fire...Though the logistics of actually carrying all of it is a bit screwy in and of itself (seriously, you normally only have two hands with which to drop them).
Perhaps the most true-to-form example of this trope (at least by the old name, Ain't No Rule) is that while the state of "Dying" is explicitly defined in the rules as far as what actions are acceptable, the state of "Dead" has no restrictions. There Ain't No Rule preventing a freshly-killed player from standing up and continuing the fight. Amazingly, this turns out to accidentally be patched by a literal reading of a completely different rule — since a dead player has -10 HP, and -10 is less than 0, dead players are technically "incapacitated by nonlethal damage" at all times.note This is, of course, unnecessary, as Rule Zero means the DM can just say "that doesn't work and you know it", but if you ever get into a fight with a Rules Lawyer...
There's no official restriction preventing you from using the spell True Creation to make planet-destroying quantities of antimatter.
An intentional case was mentioned in the 3.5 Draconomicon, when discussing vampiric dragons. The text explicitly noted that they still had the usual vampiric weakness of being unable to enter a dwelling without an invitation. It then went on to say that said restriction absolutely did not prevent a vampiric dragon from smashing the building in question to pieces and picking its victims out of the rubble.
The various settings tend to have in-universe cases somewhere in all the history and organizations. For instance, House Jorasco healers are not supposed to treat without payment in money... but there is nothing hindering them from lending the necessary money and then setting a task as repayment in kind for the loan.
In universe, the infamous Wish spell. This spell can be cast by high-level wizards, or can be granted by a few select creatures (like djinn), but they should always be met with caution. It is explicitly stated in the rules that wishing for anything too powerful can result in a perverted or partial wish fulfillment. Too careless wishing can result in getting the exact opposite of what was intended, depending on the maliciousness of the creature and/or the DM. For example, when wishing for a mighty artifact, the caster might grant you the artifact...by teleporting you into the tomb where the artifact is located, in the middle of its undead guardians.
That being said, the spell description in the Player's Handbook does include a list of effects that the DM is supposed to let go through as intended by the character's player. Furthermore, this trope is also the reason why Wish's clerical counterpart, Miracle, is considered to be somewhat safer, as Miracle is mechanically treated as a request to the cleric's deity to intercede on their behalf - and if the cleric asks for too much, the deity simply refuses the request.
In the universe (or multiverse) there's also the case of the Deal with the Devil (more or less literally). These vary, but may involve a Magically-Binding Contract that the fiend itself also has to follow, but which will definitely be written with loopholes to turn against the mortal party — at least as much so as the fiend can make it, and they'll typically have centuries of experience. Both the Lawful Evil devils and the Chaotic Evil demons do this. (However, in an interesting interpretation, some guy who thinks about this stuff a lot claimed that Lawful Evil creatures will follow the spirit of the contract, not just the letter, since twisting the wording would be Chaotic. This is still presumably meant to allow a higher-level Loophole Abuse. However, this is not the way it's usually seen.)
In an earlier version, there was an item which made the wearer immune to death. Not death-effects. Death!
Practically every rule in 5th Edition is open to discussion. Some examples include (and some may also apply to other versions):
The list of weapons you're proficient with states which weapons you know how to use, but not HOW to use them. Rogues in 5th Edition cannot use a club, but there's no rule saying they cannot hold their shortsword by the blade and use it to whack the enemies as if it was a club.
This is basically what medieval knights did when fighting other knights in platemail. The blade couldn't pierce the armor, so they used their swords as clubs instead to much greater effect.
Nowhere in the rules does it say that you have to actually fire an arrow to deal damage with a bow. Of course, it's assumed that a player who wields a bow would fire arrows from said bow, but the rules don't specifically state that this is a requirement.
They don't state that you have to use a bow as a ranged weapon either. A Longbow is still a Longbow, even if you use it to hit your enemies in melee, so according to the rules, it still deals full damage, not just 1 (Improvised Weapons are anything that doesn't outright resemble a common weapon-type. A Longbow will always resemble a Longbow which is a common weapon-type, thus preventing a Longbow from being an Improvised Weapon, and thus keeping its damage to 1d8 or 1d10 instead of just 1).
The rules aren't specific about how to actually use alchemical items, meaning you could easily get away with administering a vial of Holy Water to an undead or Acid to the guy you just beat up in a bar-fight. This way, you can save the vials for later use (like making your own alchemical items) or sell them and get a little money back.
The alignment table is a bit ambiguous at times. Particularly, it doesn't say that a Lawful Good Paladin (the typical paragon of all that is good and just) cannot start a crowdfunding campaign to help a village...using the villagers' own money! The rules just say that Lawful Good characters have to act according to local laws, be good towards others and bring evildoers to justice.
Furthermore, there's no rule saying that a Chaotic Evil character cannot have sympathy with the people he wrongs...or donate to charity.
Due to the fact that alignment-restrictions on classes don't exist in 5th Edition, Paladins are allowed to be Chaotic Evil but still serve justice and protect the weak (Oath of Devotion), while Warlocks are allowed to be Lawful Good mages whose powers come straight from Hell.
In the CCG EVE: The Second Genesis, one of the main ways to gain money (used to play further cards) is location cards. One such location has the effect "When this card comes into play, sacrifice a location". The officially sanctioned loophole around this is to play the card into an uncontrolled region. Because the region is uncontrolled, the location is uncontrolled too and the effect does not activate...
Illuminati had a particularly legendary example during its first tournament. The final match dragged on for a long time, until one of the players offered half the prize money if his opponent would forfeit just to end the stalemate. They shook on the deal...and then the first player used the card "I Lied"◊. The judges ruled that the move was well within the spirit of the game and, over his opponent's vociferous protests, declared him the winner.
Long-running Canadian strip cartoon Larry Leadhead deals with the trials and tribulations of the tabletop wargaming community. Practically every character has resorted to Loophole abuse and Dave is a particularly nasty example. Many actual examples of competitive gamesmanship encountered by the authors have been immortalised, or at least made notorious, in the form of strips.
Chaos Orb can take out of play any card(s) it lands on after you flipped it in the air. This rather unusual method of use led to many exploits:
One of the most (in)famous examples of Magic rule bending involves this card: One clever player TORE UP his Chaos Orb and sprinkled the pieces all over his opponent's playing area, thus effectively removing most of those cards from the game. The tournament judge ruled the maneuver legal, as nowhere did it say the card had to be in one piece. Don't try this yourself, though: an official ruling in 1994 declared that tearing up the card made it "marked" and you would lose the match for playing with a marked card. You would then be required to replace it with another Chaos Orb before the next round started or you would lose that match for illegally changing your deck configuration. Loophole Abuse cuts both ways. This was subsequently parodied in Magic: Unglued with the card "Chaos Confetti". Ironically, errata for that card explicitly ruled that you couldn't not tear it upby tearing it into "one piece".
The other loophole was for the opposing player to catch the card in the air then either hold on to it (thus it never landed), or drop it on any card they choose. Errata for the card eventually specified that you couldn't interfere.
When used as intended, Chaos Orb spawned another loophole: players would spread their cards out over a ludicrously large area so Chaos Orb couldn't touch more than one when it landed, or would lean their cards against things so that it was impossible to land on top of them at all. A ruling has since been made that you can't rearrange your cards after Chaos Orb enters the game. Also, you must not have your cards stacked or in places where your opponent can't read their name or count them.
Eventually, Wizards gave up and simply straight-up banned the card in all sanctioned tournament play, and ceased to produce cards involving physical interactions and dexterity outside of the tournament-illegal Un-sets.
Another possibly apocryphal tale about the card is that one player put all his cards into magnetic card sleeves and played his cards underneath the table.
An urban legend claims that in one tournament, a player cast a spell with the effect "Target player loses the game", then pointed at a completely different table and said, "That guy." You can't do that, even if nothing in the rules state the target must be in the game you're playing. That's not something necessary to state explicitly. You can't cast a Lightning Bolt at a player in another game either, or cast Control Magic on one of his creatures, or Counterspell one of his spells.
And just like with the Chaos Confetti, Wizards of the Coast make fun of such urban legends with their "un-sets". In Unhinged, there is a card that specifically lets you destroy any silver-bordered card (only the cards in the joke sets have silver borders, regular cards have either white or black borders) in any game that you can see from your seat. Some players have used this to destroy cards from completely different card games because they are still, technically, legal targets as long as they have silver borders. And with the right card, you can change the card so it affects black/white-border cards instead of silver-bordered cards and set it so that it affects all cards that you can see, allowing you to wipe out entire tournaments.
The cards of the Wish cycle specify "You may choose a card you own from outside the game and put it into your hand." This doesn't require it be a Magic card, so what's to stop you from grabbing an UNO Skip card, or Prof. Oak's New Theory? If you don't want to be that ludicrous, why not pull joke cards into serious games? (Errata for tournament purposes limit legal targets to cards in your sideboard, and the Comprehensive Rules do specify that "card" refers exclusively to Magic cards.note By which we specifically mean cards made for Magic: the Gathering. Bringing in Yu-Gi-Oh! Spell Cards printed before 2004, back when they were called Magic Cards, is of course forbidden. But you don't have to tell anyone that.)
The card Mindslaver had to have an entire rulebook printed for its original incarnation due to players using it to do things like forcing their opponent to concede the game. In the some two dozen sets that have come since then, only three other cards have ever used those rules (those cards being Sorin Markov,Worst Fears, and Emrakul, the Promised End).
An example from the game's story: Only a small proportion of individuals have the ability to freely cross the multiverse, and the Planar Bridge appropriated by Tezzeret can only transport non-living matter. How does Tezzeret's boss work around this? With a vast army of technically-non-living zombies.
"That's not the purpose of [Go Up A Level cards,] but it's so vile and Munchkinly that we love it too much to say no." Steve Jackson Games, on whether Go Up A Level cards could be used on enemies to provoke monsters that ignore characters below a certain level.
People holding as many cards as possible in your hand and doing whatever they can to prevent others from noticing that they're holding more than five are cheating. Contrary to what some urban legend claims, it's not legal to cheat in Munchkin.
Early versions of the Loaded Dice card did not specify that the value you choose to replace that of a die roll had to be between one and six. And there are plenty of cards to abuse this with, like one monster that gets a bonus to its level equal to the roll of one die.
There's no rule anywhere saying you have to use a six-sided die. It's usually just written as "Roll a die". One card specifically says "Roll a die. Any die."
Munchkin is made for this. Literally. The rules are full of ambiguities, because it's supposed to recreate the experience of playing with (and as) a rules-lawyering, loophole-abusing dyed-in-the-wool munchkin. It may not be legal to cheat, but you're encouraged to take advantage of every ambiguity possible and if you can convince the others (or at least the owner of the copy being played) then you're free. The "legal to cheat" legend comes from another Steve Jackson Games card game, Illuminati, where it really is Not Cheating Unless You Get Caught, because why the hell would ancient conspiracies play by the rules if they didn't have to? (A munchkin's true power comes from abuse of the rules, not just ignoring them, after all.)
A robot-class player or NPC in Mutant UA could have drones as an "option". Maximum would be 4 without any penalties for too many options, but drones could have their own options, deliberately so for the sake of being useful, but nothing stated they couldn't have drones as well. Cue infinite horde of massively powerful drones! (Although rule 0 almost always stops this as it's crazy-powerful.)
In Ninja Burger, one card allows you to use your highest skill in any skill check, so long as you can think up a plausible explanation for why you'd be able to use that skill to solve the problem. For sufficiently creative players, it's a total Game-Breaker...if the other players at the table let them get away with it.
Pathfinder has the Ferocity special ability: a creature with Ferocity (usually a monster, it's very rare among PC races) doesn't fall unconscious and start dying at negative HP, instead gaining the staggered condition (limits actions per round to one standard or one move action, other quicker actions aren't affected) and losing 1 HP per round until killed when its HP drops too low. The problem is that the description didn't take nonlethal damage into account at all, meaning that by the rules as written, a creature with Ferocity cannot fall unconscious from lethal damage but can be neutralized with 1 point of nonlethal damage, making the ability totally useless since anyone can deal nonlethal damage with an unarmed strike or by taking a penalty to attack rolls with any melee weapon. Some players even say that a creature at negative HP obviously has more nonlethal damage than current HP and then should fall unconscious even with Ferocity. Needless to say, this subject has been quite debated on forums.
The list of errata and clarifications for specific situations for the Pokémon Trading Card Game, known as the Rules Compendium, is comparable in length to the Magic: The Gathering one and requires hours to read.
Outside of the Compendium, there are also some rules for tournaments not directly related to the card text itself. Unique to the Pokémon Trading Card Game is a rule stating that artwork for card sleeves must have a continuous solid-color border (which was previously a rule banning all artwork and restricting card sleeves to transparent or solid colors, then changed to allowing only official Pokémon Company issued sleeves). This was due to rampant subtle marking of cards by taking tiny trims off the sleeves' edges, sometimes using artwork that made it hard to notice by opponents.
There are a few cards that ask opponents to play RockPaperScissors. In response, some players learned techniques to detect which hand gesture the opponents will use (techniques used in official Rock Paper Scissors competitions), allowing them to consistently win except against someone who knows these techniques, too. The designers didn't realize players would go to these lengths, and as a result, there was a two-fold Obvious Rule Patch: The first is that the only allowed means to play Rock Paper Scissors in Pokémon TCG tournaments is to write down the choice under the table and present it simultaneously with the opponent. The second is that there are no longer any Rock Paper Scissors cards that are tournament-legal.
An in-universe example: following the Age of Apostasy, the new Ecclesiarch Sebastian Thor declared the Decree Passive, in which the Ecclesiarchy was forbidden to maintain men under arms. Thor's predecessor's Bodyguard Babes, the Brides of the Emperor, were allowed to continue operating as the Adepta Sororitas because Thor knew the Ecclesiarchy needed a militant arm and internal regulation. They were not "men" under arms, even though it violated the spirit of the decree.
The FAQ articles have had to correct some in the past.
The Swooping Hawks's Intercept rule reads "the unit never requires worse than a 4+ to hit an enemy vehicle", which means, for instance, that the WS 4 Swooping Hawks could hit a WS 5 Venerable Dreadnaught on a 4+ instead of a 5+ as the normal Weapon Skill table would indicate.
An Ork list that was designed entirely around exploiting the wound allocation rules in fifth edition by giving every model in every unit different gear was briefly popular on the tournament scene.
Units may fire out of the windows of a building. The rules don't prevent units with "barrage" type weapons, like mortars, from firing through the roof of the building their operators are in.
In an older edition, you could hold any number of your units in Reserve, so that they came in later during the game. Nothing said you couldn't do this to your entire army, thereby denying your opponent a first turn AND strategic deployment as he won't even know how your units will come in. However, one savvy player managed to turn this loophole on its user: Nothing said you couldn't just deploy your entire army along the enemy's table edge (where reserves come onto the board) and prevent his units from ever entering the gamenote Any unit coming in from reserve must "move onto the board" with their movement phase allowance. But units cannot move through an enemy unit, no matter the circumstance. Also normally you're restricted to your own deployment zone, but in this case the other player used Infiltrators, which had to be set up 12" away from any enemy with line of sight to it. Since the opponent had no models on the board.... Later editions decided to make this entire process shorter by making you automatically lose if a turn ends and you have no units on the board (Reserve units, unless specifically stated, don't come in until turn 2 at the earliest).
Related to the above, units normally have to remain in coherency. However "coherency" is only defined as "being within 2" of the nearest model". This led to a tactic known as "daisy chaining", whereby the entire unit is stretched into a single file line with 2" between each model. Technically no model is more than 2" from the nearest one (especially when the definition of "nearest" is vague at best). This tactic is largely used for area denial (as in the above example, using a single unit to cover the entire edge of a board) or if units have different movement speeds then the ones moving faster can proceed to charge the enemy while going through the chain, then "dragging" everyone else along as technically they were one unit and the entire unit charges, making them invulnerable to enemy shooting in the next turn, as you can't fire into combat. The most hilarious use of this was in 5th edition, where Canoptek Spyders could generate a single Scarab Swarm base and attach it to an existing unit. Nothing ever said that the base had to be near the Spyder that created it. Cue players using the daisy chain to literally "walk" an entire unit of scarabs to the enemy's deployment zone. On the first turn.
One pretty infamous example of rule abuse in 40000 was the so-called "Fish of Fury" tactic. A Tau player would park two of his Devilfish in a V-shape in front of two Fire Warrior squads. Opposing fire couldn't hit the warriors without going through the hover tanks, but the warriors themselves could fire "under" the very transports that were shielding them, and melee units couldn't assault the tanks at all, forming a sort of unassailable mobile bunker for the infantry. While some really firepower-heavy lists could swat away the APCs and deal damage, it rendered melee armies like the Orks and Tyranids utterly useless, which is bad seeing as being attacked in melee is the Tau's main weakness. The tactic was a massive Game-Breaker and it dominated tournaments for ages until the rules for hover vehicles were mercifully changed. It got so bad that in an attempt to distance themselves from "Fish of Fury" stigma, some Tau players completely removed Devilfish from their lists (even though the Tau army really needed them in their intended function) and slogged their squishy ranged infantry across the field on foot.
One infamous incident most often cited as when GW no longer had any proofreaders was the entry for the Nemesis Force Falchions in the 5th edition Grey Knights Codex: The rules for the Falchions state that they grant +1 attack. This is because in-lore they are always wielded as a pair. But because the rules specifically state that you get "a pair" of Falchions, this means that technically you have two identical weapons, which also grant +1 attack. This meant that the Falchion option actually granted +2 attacks...that anyone in the army could take. Suddenly every single Grey Knight in Power Armor could be wielding a Heavy Bolter (with the Psybolt Upgrade) and each had more attacks than most units could put out. The FAQ later clarified that the +1 attack wasn't the weapon's special ability but rather for having 2, and the 7th edition update completely eliminated the issue by not giving the Falchions any special abilities from the standard Force Sword (you still get a pair of them).
Deathstrike Missiles are one particularly Awesome, but Impractical Imperial Guard vehicle that's more-or-less an ICBM launcher mounted on a truck, boasting a spectacularly large blast zone, absurd amounts of damage to anything caught within it, and previously unlimited range. Yes, unlimited. Its minimum range already rendered it difficult to use on most tables, and unlimited is simply overkill. Nothing states that you necessarily have to fire it at the same table, however, and in theory a Deathstrike launch could hit another game, even across real-life continents. See this story for amusing results of cross-Atlantic carnage that can ensue if everyone feels like playing along. It has since been changed to a limited 200" range, still far enough to reach anything but the largest table, but not far enough to hit another real-life building unless everyone agrees to it.
An in-universe one for the Bretonnians (whose hat is chivalry and Honor Before Reason), specifically the duchy of Carcassonne. No self-respecting Bretonnian lord would let mere peasants fight if he's not there to supervise, not would he disgrace himself by hiring mercenaries. So in order to allow independently-operating warriors move around as necessary, they're given a sheep to protect, because shepherds need to be able to defend their sheep against predators like wolves and beastmen and orcs and Chaos cults. And while a shepherd' pay is very low, nobles tend to get strangely clumsy about dropping coin-filled purses around these "shepherds". Some mercenaries end up adopting the sheep as a mascot, others eat it.
Similarly, Bretonnian knights consider ranged weapons to be fit only for peasants, and forbid guns to be used on Bretonnian soil. The Bretonnian navy, on the other hand, fill their ships with enough cannon to make an ork happy, since they aren't on soil (and Bretonnian's major port would very much like to be able to use cannons to defend their harbor).
One of the lowest-level spells in Warhammer Fantasy Roleplay made an object glow brightly for an hour, and then disappear out of existence. Putting a one-hour countdown on a huge and unfightable enemy seemed like a fair trade to many players.
During the rough early days of Warhammer: Age of Sigmar (before Games Workshop started taking it seriously and implementing things like points systems), the changeover lists for the audience's old Warhammer armies were rife with this due to their generally free-wheeling and jokey tone. For example, characters that gained bonuses from moustaches or beards didn't specify they had to be real. Lax definitions didn't help; for example, because armies were defined as 1+ warscrolls, it was hard to tell whether you legally needed actual models or if you could just show up with a single house and win because there were no rules for destroying it. Other rules were somewhat carelessly edited, with a literal interpretation of the High Elf repeating bolt thrower's shots table meaning that you could fire 72 shots per turn instead of the much more reasonable 12 that the designers presumably intended. The apex, however, had to be Fateweaverhammer. Kairos Fateweaver allowed you to pick the result of one die roll per game. The Skaven Screaming Bell had a table where the results of its power varied by your roll on two six-sided dice, with a joke entry at 13 reading "you win the game" (since 13 is a sacred number to Skaven). And rules disputes were supposed to be settled by a roll-off. So, you'd bring one Screaming Bell and as many Kairos Fateweavers as would fit in your deployment zone, use one to declare that the result of your first Screaming Bell die roll was 13 (after all, it never says the number you choose has to be on the die), and the rest to win an endless string of rules dispute roll-offs when your opponent inevitably challenges this interpretation. Most of these, admittedly, were thought experiments critiquing the initial release's slapdash mechanical execution and were never actually brought to the table.
There are a lot of infamous combinations which resulted in continuous loops in Yu-Gi-Oh! that result from this. The vast majority of them involve exploitation of the ruling that, except in very rare cases, a monster's effect is "reset" when it is flipped face-down or removed from the field temporarily, allowing you to reuse the same effect multiple times in one turn, with the right setup. There are even entire decks constructed around this.
Before it was banned, the card Last Turn was the subject of quite a few loopholes, mainly because it didn't negate monster effects while it was in use. To wit, when it's activated, both players choose a monster to be on the field (the activator from their field, the opponent from their deck) and battle. Whoever has a monster remaining on the field after the battle wins, otherwise it's a tie. Thing is, the monster left on the field doesn't have to be the one the player chose for the battle, and the card doesn't negate monster effects, so if you have a monster on the field that can prevent Special Summons (thus, preventing the opponent from getting out their chosen monster), or one that can Summon out a monster when destroyed (thus leaving you with a monster after the battle), you can easily screw over the opponent with it.
Lava Golem is a card that requires you to Tribute two of your opponent's monsters to summon it to your opponent's field. Because Lava Golem's effect is technically a cost to play it, rather than an effect, and because it technically doesn't destroy the tributed cards, it's attained a level of fame as one of the only monsters that can kill literally anything, regardless of circumstancenote There are still exceptions to its effect, such as Fog King, who prevents Tribute Summons from taking place at all.. This equally applies to any monster that Tributes your opponent's monsters to Special Summon itself, such as The Winged Dragon of Ra - Sphere Mode and the Kaiju archetype.
A couple of cards were introduced with the ability to return from to play from the graveyard under certain conditions/costs, but then banished when they left the field to prevent them from coming back more than once. Later, the Xyz mechanic gave players the ability to easily move cards from the field to the graveyard without ever triggering effects which would otherwise trigger when they left the field, by using them to create Xyz monsters, then detaching them.
Speaking of Xyz monsters, Xyz monsters have "ranks" instead of "levels" unlike most other monster cards in the game. This allows them to dodge effects that depend on levels such as Gravity Bind. (Notably, this is actually something of a nerf compared to the alternative, which would enable players to use Xyz monsters as material for other Xyz monsters with no external methods.) Link Monsters have a similar thing going on.
The D/D/D archetype uses this as a primary mechanic. The cards are aided by the Dark Contract series of cards, which act as Deals with the Devil: you're given effects that let you pull off combos or summon monsters, but must pay 1000 LP each turn, for each active Dark Contract you're using. The twist is that there are cards to destroy these cards after you use them, but before you have to pay the price, letting you get off scot-free. Further, some of the D/D/D monsters they bring out actively subvert the LP cost and let you use the cards with impunity. The most obvious example would be D/D/D/ Oracle King d'Arc, whose effect lets you gain LP from the Contracts instead of losing them.