Most of it falls into three categories: broken, very broken, and holy God-Emperor what is that abomination.
— RPG.net combat optimiser Jon Chung, on the Scroll of the Monk for Exalted
Game Breakers in Tabletop RPGs. While any option or combination of traits not explicitly denied to the players will get tried, only a fraction of these builds see actual use due to GM oversight.
Dungeons & Dragons 3.5 has this in spades. Almost anything can be a game breaker if taken to a great enough extreme. Characters can instantly end every encounter with a successful Diplomacy check which it is possible to render impossible to fail at a very, very low level. This is only the tip of the iceberg; even without exploitative min-maxing, all the spellcasting classes are almost hopelessly broken by seventh level, and canny players can break the game with low-level spells like Color Spray, Sleep, and Glitterdust. The so-called "save or suck" spells all instantly incapacitate monsters or otherwise render them unable to fight, and many of these spells exist even at the lowest levels, allowing spellcasters to bypass the entire hit point system and kill monsters with a single roll. Worse, spellcasters also have huge levels of flexibility and can make themselves effectively invincible against many ordinary attacks, have near-infinite mobility by mid-levels, have the best offensive and defensive capabilities, and are the best at making magic items, which themselves can often act as game breakers or exaggerate a character's game-breaking abilities. Even non-spellcasting classes can frequently do incredibly broken things, such as dealing more damage than any monster has hit points in a single round by mid-levels. As is noted in the unofficial (but widely accepted) tier list for the game, the third tier is not an insult to characters. A third-tier character is capable of defeating any monster in the game; they simply are not God.
Before reading any of the below, its worth noting that, unlike with video games, its common accepted practice for the DM to limit the options available to players to a subset of what is available and to disallow the Loophole Abuse that most of these builds are built on. And if the players do end up building a completely broken character anyway, they'll generally work with the DM to make adjustments so the game is still fun for everyone. So unlike with video games, its okay for a Tabletop RPG to risk combinatorial explosion by continually giving the players more options.
Annoyingly, some of the monsters fall into this category as well against unprepared players. Many monsters have instant death or incapacitation abilities which can take a PC out of combat or, in some cases, even turn them against their allies; enemy spellcasters are a particular nightmare, due to having access to every broken ability that the players have (and, thanks to polymorph and similar shapechanging abilities, players have access to every broken monster ability as well). High level combat in 3.x edition (including Pathfinder) is often described as "rocket tag" for this reason - whoever fails their saving throw first, loses. Assuming the ability in question even allows you to roll a saving throw. Feats which improve your ability to act first in combat thus are viewed as extremely powerful, simply because very frequently, it gives you an enormous edge by allowing you to take out one or more enemies before they can even act - and prevent them from doing the same to you.
Another particularly special example is the Omniscificer. There is a spell which allows you to share the damage you take with others, and it is possible to cast this spell in both directions; because each person receives half the damage given, if you cast this on four people taking half the damage of a fifth person, and in turn dealing back to that fifth person half the damage they themselves receive; as you would then be receiving back a quarter of the damage you originally took from each of the four people, you thus have created an infinite damage loop (so long as you have dealt yourself at least 4 points of damage - say, by jumping off a 40 foot cliff), causing you to instantly take an infinite amount of damage as the damage washes back and forth between you and your helpers. Ordinarily this would be extremely fatal, but there is another spell which allows you to stay alive for a short period of time despite being reduced to -10 or fewer hit points (which would normally kill you). There is also a spell called masochism which causes you to gain a +1 bonus to all your skill checks per 10 damage you took in the previous round; as you have taken an infinite amount of damage, you now have a literally infinite bonus to all your skill checks, allowing you to succeed at any skill check automatically. Better still, there are (extremely large) penalties you can take to many skill checks to instantly take certain actions, and other skill checks are by their very nature instant (such as knowledge checks). This means that the Omniscificer can, among other things, instantly succeed at every knowledge check possible and thus know everything that can possibly be known from a successful knowledge check. They also have an infinitely large diplomacy (and bluff, and intimidate) check, meaning that they can convince anyone of anything, and with the proper spells, can communicate with anyone (including the gods), meaning that they can convince the GODS of anything. Now, all of this is impressive, but they are still stuck in an infinite damage loop; however, they can simply dismiss the spell creating that loop, and then fall over into a bucket of water and voluntarily fail a drown check. Due to the way that drowning rules work in D&D, when you fail your first drown check, your hit points are instantly set to 0... meaning that it heals you from -infinity hit points to a much more tolerable 0 hp, from which you can easily be resuscitated with any manner of curative magic (or alternatively, a contingent cure minor wounds spell).
Many of these to be found in Dungeons & Dragons 3.5, a few of which do not even require sourcebooks outside of core (Pun-Pun is only the most famous as he basically amasses all of the others' powers). A full list of these may be found here along with explanations. Yes, the official D&D forums have an entire board dedicated to the pursuit of the most hilarious/demented Game Breakers ever (though the logic behind many of them is equivalent to "But the rules don't SAY dead people can't keep fighting and taking actions!").
And it's not all about character design or game mechanics either. For instance, a 10 foot ladder is cheaper than two 10 foot poles, allowing for an infinite money loop and infinite firewood. (Think about it.)
Another Tabletop Games example: The haste spell in Dungeons & Dragons version 3.0. Originally redesigned the way it was to "show off" the new action rules, designers learned the hard way that there was such a thing as an action "economy" in their resulting game... and whoops, they broke it. Nerfing this spell was arguably one of the primary reasons for the creation of 3.5.
To make this one step worse, the "speed" armor enchantment permanently duplicated the haste spell and was cheap which wouldn't have been so bad except then the Arms and Equipment Guide established that armor enchantments could be added to bracers of armor which could be worn by characters who don't normally get to wear armor. Every mage in his right mind bought a pair as soon as he could afford them, as an item that grants +1 armor bonus, +4 dodge bonus, AND lets you cast twice as many spells per round without having to ever take the action to cast Haste is a steal at 16,000 gp.
D&D 3.0's Harm, full stop. A touch attack that leaves a target with 1d4 hp. What this evidently means is that the more hit points a target has, the more damage it's going to take.
It did the same in prior editions: 3rd edition simply put in a Hit Points system that broke Harm completely compared to all the other damage spells. While the Hit Points of your average non-Mook increased about fourfold, all the damage spells did the same damage. Result: Fireballs and lightning bolts lost 3/4ths of their effectiveness, Harm lost none.
Yet another D&D 3.5 example: the Hulking Hurler Prestige Class. The damage of a thrown object is proportional to its mass and limited only by your carrying capacity. If you qualify for the class at all, it's a one-hit-kill. Optimized HH builds have been known to do TRILLIONS of damage.
The supposed 'balancing factor' for the Hulking Hurler was that it required the character taking the prestige class to be Large size or larger, which put it out of reach for most PCs without taking a truckload of monster hit dice or level adjustment. It probably wasn't meant to be used by player characters at all, but players found ways around the restriction (such as enlarge person with permanency).
Or the goliath race, which counts as Large for some things and can get a barbarian racial substitution level which increases their size to Large while raging. Which means for the low, low cost of a +1 level adjustment you may now play your Hulking Hurler, Incredible Hulk-style (as long as you happen to be actively raging the exact moment you level up, every time you level up, as that is a prerequisite to taking any levels in the class in the first place).
Another D&D version involves what is typically dubbed the locate city bomb. There is a spell called "locate city" (a harmless divination spell), which has a radius effect of 10 miles per caster level. One then uses an obscure series of feats to first give it the Cold subtype, then deal 2 Cold damage to everything in the area of effect, then change it to an Electric type spell. You can then use another feat that gives an Electric spell a Reflex save, allowing you to apply the Explosive Spell metamagic to "locate city", forcing a second Reflex save to avoid being blasted to the edge of the area of effect. Failing this save will deal 1d6 damage for each 10ft travelled, allowing someone to instantly wipe out a whole city of commoners with no collateral damage (except for the blood splatters).
One noted problem with this spell is that the same very unusual area of effect that gives it such a noteworthy large area also makes it definitionally two-dimensional (the spell explicitly affects a circle - not a three-dimensional area like a sphere or one of the normal areas of effect). The damage is based on the distance those within the spell must be propelled to be ejected from the area - which depending on the elevation of the spell and their height may be just a few inches or feet straight up or down, if they're affected at all. The other problem is, even disregarding that, hitting an obstacle immediately arrests the targets' movement, and the first 10' of falling is nonlethal damage, so many may only suffer 1d6 worth of bruising against the nearest wall/tree/fence/etc.
The main advantage of locate city is that it's a very accessible spell (on four major spell lists as a 1st level spell) and has excellent scaling. There are several other options that characters gain access to later or with a bit more effort and worse scaling without the potential problems with locate city; i.e. 1 mile/level versus 10 miles/level. Although a mere 10% of locate city, it should be noted that on average the damage dealt by a single mile in this fashion is roughly four times the hp of the biggest, baddest dragon a party is likely to ever see before epic levels.
A simple 3.5 spell which is not high level, does not appear exclusively in an obscure sourcebook (it's in the Player's Handbook), and doesn't require a cheesy combination to work is the level 3 Bard spell 'Glibness'. In a game system where +4 or +6 to a roll is considered a considerable bonus, Glibness gives +30 to your bluff checks for its duration (10 minutes per caster level, a minimum duration of over an hour). The penalty to your Bluff skill check for telling a lie that is completely and utterly unbelievable ("I am the Moon.") is only +20 to the opposing Sense Motive check. With Glibness, you can quite easily convince a king that you and he were actually secretly swapped at birth and that by all rights he's sitting on your throne. This is the kind of simple, elegant spell that can make a GM go "What the ^%$##*@!^?!". Glibness' power was highlighted to great effect in an Order of the Stickstrip. Yeah, that describes it nicely. The intended balance is that Glibness only provides its bonus for the purpose of telling lies, but as has been shown, that's quite broken enough by itself.
Glibness can be seen as a subset of the entire game breaker that is otherwise known as the Diplomacy skill. Under the rules as written, it requires a result of 50 to turn someone willing to take risks to hurt you (Hostile) into an ally willing to take risks to help you (Helpful). Considering it's legally possible to build characters who get +72 to their Diplomacy rolls by level 6, in theory you need never carry a single weapon nor fight anyone in your life, since you'll only have to open your mouth for roughly 10 seconds to enlist the help of virtually anyone who wants to hurt you.
Of course, you have to have a common language (or other way to communicate) and the things trying to hurt you have to be smart enough to understand the concept of "friend" (and preferably not in a fundamentallyunhelpfulway), so it's not foolproof.
Blink, Ethereal Jaunt and similar spells which let the caster pass through walls and ignore attacks have been the bane of many an unseasoned DM. Heck, just about everything on the Story Breaker Power page is available as a spell.
It's hard to find a use for Invisible Spell (viewers cannot tell that your spell has taken effect) that isn't overpowered. Common uses include Invisible Summon Monster, Invisible Fog Cloud (only obscures the vision of creatures who can see invisible things), Invisible Invisibility, and Invisible True Resurrection.
By combining feats from multiple sourcebooks, it's possible to reduce the cost of Bestow Power (transfers psionic energy to another creature) until it can transfer at greater than 100% efficiency, allowing a character to recharge their psionic abilities between fights. This wouldn't be as notable if psionic characters didn't have the ability to boost the strength of their powers by expending larger amounts of energy (meaning that a character using this trick can "go nova" in every fight with no consequences).
To put this one into perspective, there is a ranking of the classes based on power and versatility, from tier 1 (can solve almost any problem easily) to tier 6 (no useful abilities). Druids are of course tier 1, and there are no non-spellcasters above tier 3. As an example, the guy who built the system showed a variant where all spellcasting became extremely difficult, knocking most spellcasters from the lofty heights of tier 1 and 2 down to tier 6. Druids however were still at the high end of tier 3. Why? A single class ability of course: Wild Shape, an ability that is in and of itself more powerful than a Fighter's whole class (indeed, a Ranger variant with a nerfed version of Wild Shape as its primary ability is at the low end of tier 3). Actually, twinked out animal companions are stronger than Fighters. There's a reason why CoDzilla (Cleric-or-Druid-zilla) became a DnD meme.
And once you get out of core, there's the ludicrously overpowered Planar Shepherd, which happens to be custom made for Druids (and possibly the only Prestige Class strictly better than more Druid levels). Other gamebreaking prestige classes include the Dweomerkeeper, famously used in the "Cheater" (Chosen) of Mystra, which could circumvent almost all all the restrictions on Wish and Miracle, and use both multiple times per day.
No discussion of broken prestige classes is complete without the Player's Guide to Faerun incantatrix. First, the requirements: third-level spells, three skills you were already taking, a feat you were already taking, and a feat that you can actually buy. Most casters qualify by accident. It gives full spellcasting progression, which means it's automatically better than continuing with most caster classes. Most full casting prestige classes provide minor benefits or only run for a few levels, but the incantatrix runs for ten - and its features are some of the strongest in the game, with four free metamagic feats, applying metamagic effects to an ally's spells (or your own), stealing continuous effects from enemy casters, and a capstone so overpowered that it's normally an epic feat. Pump up Spellcraft, and you can cast all your buffs at the start of the day, and Persist them at minimal effort. Picture a 20th-level wizard with Prismatic Sphere, Shapechange, Superior Invisibility, True Seeing, Haste, Freedom of Movement, Globe of Invulnerability, Elemental Body... all at the same time, all day long.
Finally, in our survey of D&D options which don't rely on an unforeseen combination of feats and/or spells to break the game, consider the spell Shivering Touch from the sourcebook Frostburn (and well you should, since the game's creators clearly did not). When you cast it, you touch your target (usually not hard since D&D's combat system tends to focus around getting through armor to inflict damage rather than simply touching them - though spellcasters or creatures with certain exotic or class-granted defense bonuses may have very high touch AC). That target then suffers between 3-18 points of damage to its Dexterity. Because the aforesaid monsters generally have a low Dexterity, depending on how well you roll this will actually penalize an opponent's AC by up to -5 if you take their Dexterity to 0, and also render them unable to move. The phrase 'sitting duck' then applies to your opponent. As an added bonus, unlike most other seriously powerful spells in 3.5, Shivering Touch does not allow a saving throw against it. The only beasts that stand a chance of avoiding death by clumsiness are those with spell resistance. Not bad for a spell which any cleric or wizard can cast from level 5; in some spheres this spell is called the dragon killer. And that's even before you look into things like applying metamagic to it.
Want to break the game with just two spells? Cast Contigency, make your contigent spell Celerity. Congratulations; the next time somebody threatens you, you get a free standard action to do whatever you want. You can even cast Twinned Celerity. Then use the extra actions from Twinned Celerity to cast TWO Twinned Celerities. Sure, you get dazed next turn, but if there's an encounter you can't finish or escape when given four free standard actions, it's time to give up on the whole "wizardry" thing.
Polymorph. Any. Object. All but the most frugal interpretations of this spell are absurdly broken, particularly considering that some interpretations allow for removal of the HD limit to Polymorph (an example of the spell is turning someone into a stone, which has no HD), or transforming a creature repeatedly to make any form permanent. How do you feel about permanently turning the party fighter into a giant, or the party wizard into an ethergaunt with 27 Intelligence? Plus, in a pinch, it's a nasty little save-or-die.
There is no usage of Genesis (once an epic spell, 'downgraded' to a 9th-level spell) that isn't completely broken. Free demiplane? That only you know the location of? And you can determine the traits of? Including, say, making it a Fast-Flowing Time plane? Or giving it morphic traits, letting you warp it to your will? About the only justification for it is that by the time you've gotten 9th-level spells, the game is basically over anyway.
The Erudite class in 3.5 is not broken in and of itself. It has the ability to eventually learn every psionic power there is, but this just makes it the psionic equivalent of a Wizard, whereas other psionic classes would be focused spellcasters like Beguilers or Warmages. The "Mind's Eye" series of columns on Wizards of the Coast website, however, provides an alternate class feature called Convert Spell to Power. For the cost of giving up a single bonus feat at 1st level, this feature grants Spellcraft as a class skill and allows the Erudite to use it to study any arcane spell, convert it into a psionic power, pay a small (e.g., 400 XP at 20th level) cost to permanently learn that power, and then use it at will for as long as their Mana Meter holds out. So not only is your Erudite a psionic-type Wizard, he's now also a mutant wizard-type Wizard that can spontaneously cast like a Sorcerer and isn't subject to arcane spell failure.
Perhaps even more alarmingly, the spell-to-power Erudite can even ignore costly material components.
Want to destroy the world? Pick a melee class. The metabreath feats in the Draconomicon allow a creature with a true breath weapon—which was not available to players at the time without jumping through a lot of hoops—to improve the damage/range/staying power/etc. of a breath weapon at the cost of extending the cooldown between uses, and they could be stacked with themselves. A 5th level green dragon shaman with 17 Constitution and the feats Enlarge Breath, Clinging Breath, and Lingering Breath could, in a single round, theoretically create a cloud of acid the size of the entire planet that lasted for a year or more at the cost of not getting to use his breath weapon for several years. The only problem is that anything that did survive (high-level wizards, earth elementals, etc.) would come looking for revenge slightly sooner than that.
Eschew Materials, weak ass feat or subtle game breaker? This feat will let you cast spells without having to worry about inexpensive material components, provided they cost less than 1 GP. Unfortunately most of the times won't come into play and doesn't take care of the expensive components, which most of the times are the ones you care about, such as 500gp valued Diamonds etc. Generally it is used when you don't have free hands to use or as a contingency when you don't have access to your component pouch. This feat has been used with a couple of spells to produce weird effects. Another use is casting fabricate to create really cheap things, without having to have access to the materials beforehand, basically conjuring something out of thin air; you could for example visit the astral plane (or any plane that has the timeless trait - assuming you don't have any aging problems, this is a separate but solvable issue...) and cast fabricate as many times as you can to generate 1 gold piece each time, making you rich in no time when you come back to the material plane.
The feat Divine Metamagic allowed Clerics to apply power-up modifiers to their spells in the same way Wizards can, but at the cost of Turn Undead uses for a day. This would normally be fairly weak, but it became a Game Breaker when a magical rod was added to the game which grants an extra Turn Undead attempt when used. Clerics could carry huge sacks of rods around and use them at the start of each day to cast multiple spells on themselves, extended to 24-hour duration.
D&D 2nd Edition Skills and Powers had a mage variant called Channeler, which effectively combined mage and sorcerer (you could learn as many spells as you wanted and cast them all however many times you wanted until you ran out of spell points). The only downside? You fatigued yourself when you cast a spell (and yes, you could kill yourself this way). There was an 8th-level spell called Heart of Stone that replaced your heart with a carved stone one. Among other effects, it made you completely immune to fatigue.
In the 2nd Edition of Dungeons & Dragons the Psionicist's Dimension Door wasn't limited to vertically standing doors. Open a horizontal door below your target, put the horizontal exit above them. Let them fall for a while (the disorientation effect keeps them from casting or doing anything to save themselves). This either ends with the target being cut in half by a closing door or splatting against the floor. Good fun. Meanwhile the Psi is constantly getting EXP for expending power points. That's thinkingwith portals.
D&D 4th Edition has a large number of infinite combos IN THE CORE RULES:
There is a 15th level Ranger power called "Blade Cascade," which allows multiple hits as long as the previous hit connects. This inspired game-breaking accuracy builds; one such (Kenshiro "Ratata" Orcuslayer) could kill Orcus at level 15 as long as the player did not roll a 1 (which is an automatic failure) on the d20. Wizards of the Coast quickly issued an errata stating that the maximum number of hits on the power was 5 (1 per 1.25 seconds of the combat round).'
Sleep is a first level Daily spell that knocks people out, making them vulnerable to continuous Coup de Grāce attacks. You can use Salves of Power, (which cost 5000 GP and a Healing Surge) to regain this power. And until recently, getting a -16 continuous penalty to saves was quite easy (now it's basically impossible, although you can still get a fairly high penalty to saving throws for one or two rounds).
Everyone say "hi" to the Essentials classes, mostly found in the "Hero of X" books. Their intended use: get casual/first-time players into the game with a class-build that's far easier to deal with than most. Rather than potentially dozens of powers and situational options, you typically have your Melee/Ranged Basic Attack boosted in one way or another, either increasing the damage, adding effects or letting you make follow-up attacks. On its own, this isn't particularly bad, but those classes qualify for feats that modify basic attacks further. Want to push 3 squares, impose a -2 penalty to attacks on a hit OR miss, and eventually daze at will? You can! Add in the number of items and ally class-features (especially from warlords) that allow you to make basic attacks outside your turn, and you could have a character dealing more damage per round with basic attacks than most classes deal with encounter powers.
In Werewolf: The Apocalypse it was possible, with mere hedging of the rules rather than outright cheating, to make a starting character that rolled in excess of 40 damage dice per hand, and went first in every combat round.
Even without any cheating at all, werewolves in the Old World of Darkness could spend Rage to have an extra action in a combat round. Rage replenished every time they got angry—so basically all the time.
In Vampire: The Masquerade, one of the most brokenly powerful powers was available at character creation and found at lowly Discipline level 2 of Obfuscate - which let the vampire using it become invisible. No blood or willpower spent, no roll needed. Just plain ol' at will invisibility. Now, there was a counter (Auspex, available to a handful of vampire Clans and even then they had to be at least as good at Auspex than you were at Obfuscate), it didn't fool cameras or other technological systems (not a problem if you're playing Dark Age) and until higher levels in the discipline it dropped when attacking or performing similar attention-getting actions. Still, quasi-perfect invisibility any time you want, in a game that revolves around intrigue, information gathering and general-purpose skulking around ? Sorta kinda neat.
It's not quite as powerful as all that, since you can't 'go invisible' to anyone who's actually watching you when you do it... And 'attention getting actions' include such things as: Making any kind of sound louder than nearby ambient sounds, manipulating any kind of object that can be seen (opening a door, picking up something, accidentally bumping into a chair), doing anything that would attract attention if you weren't invisible (pointing a gun at someone even if you don't fire it, dancing, making faces) and you need to concentrate to keep it active so if anything distracts you you're suddenly fully visible again. Still, with enough points in the Stealth ability and a bit of careful planning, it becomes very powerful very quickly.
A minor example is available even at character creation. A new character can put a maximum of five dots into the generation background trait, bringing his vampire from 13th generation all the way to 8th; in other words, from one step above a rank Caitiff all the way to the lower rungs of the old blood, letting him have a blood pool 50% greater than a normal starting character. Such a character can also spend up to three blood points per round, rather than just one. All in all, a higher generation rating gives a character the capacity and capability to perform actions and disciplines far beyond other vampires of greater "experience".
But perhaps the biggest game breaker, is the Tremere's Path of Conjuring Discipline. At first glance, you might only think it's good for creating personal weapons out of thin air. However, since you can summon anything you know the construction of, a generous helping of points in Science will give you the power to make (Among other things): Napalm, Gauss Weaponry, Plastic Explosives, or even Antimatter! Worse still, if you take the time to conjure the building supplies, this can be used to make larger scale weaponry like Tanks, Battleships, Fighter Jets, Mech Suits, or ICBMS. And to top it all off: You can have this build at character gen.
Not to mention that it does not take exceptional skill in biology to create blood with the upper limit being the body mass of the conjurer. Also all sorts of chemicals and compounds were available to a master of the Path of Conjuring for fun and profit.
The first edition of Warhammer Fantasy Roleplay contained several somewhat ill-considered spells, the most infamous of all being the innocuous-sounding Glowing Light. Glowing Light is a very basic Petty Magic spell used to turn any handy useless object into a disposable torch. At least, that's what it was supposed to be used for. The spell description actually just said "The object glows brightly for one hour, and then vanishes." And then vanishes. Most novice wizards considered that a one hour time-delay was a fair price to pay for the power to vaporise anything they could lay their hands on.
In GURPS someone built an advantage named M.U.N.C.H.K.I.N. that allows you to disintegrate the entire universe for 53 points in a game where a "career adventurer" is expected to start at 200 points.
"It's a cosmic attack, literally. Pulses of cosmic energy that radiate from the attacker (reaching 74 gigaparsecs in a flat second) burn out the neural system of living beings in the affected area, and remember that even the edge of our universe is "merely" about 10 gigaparsecs away from Earth. Also note that an Area Effect attack with Emanation involves no to-hit roll and simply affects anyone in the area. Furthermore, it allows victims only to dive for cover, and actually there's no effective cover since this Cosmic, Irresistible attack ignores DR. In conclusion, the user can attack every living thing in our entire universe, with 1 point of damage, 300 times per second. Have fun. 53 points."
Second Edition Exalted: In a game where defense has primacy, Obsidian Shards of Infinity Form has two scene-length perfect defense charms, one of which allows you to perfectly redirect any attack aimed at you. It lets you make and control a perfect clone of your opponent who is linked to the clonee, and command it to kill itself, knocking the opponent out. A charm to make all of these cost zero essence. These charms are almost impossible to counter, and the chance of someone having IC knowledge of them is low.
And then there's the combination of Grandmother Spider Mastery and anything that enhances perception. Grandmother Spider Mastery allows the Exalted to attack everything that he or she can see in a single action. There are charms that allow an Exalted to see everything in several hundred miles, or even everywhere in Creation. Pattern Spider Touch turns a single action attack into a move that either utterly destroys or transforms its target. The natural result of this has been nicknamed Creation-Slaying Oblivion Kick. It does, however, require Essence 7 and a cooperative Sidereal Martial Arts master, at which point killing everything everywhere isn't that far from the norm.
Actually, this can be obtained much earlier using a combination of Mentor 5, Divine Transcendence of Martial Arts, and Glory to the Most High (Basically, you can have the Master Lupo or Aesha Ura as a mentor, and you count as having 2 more points of Essence than you actually have). Granted, this is an expensive build to make, but it's still a mass destruction charm combo obtained several hundred years before you should be able to use it.
The merit Brutal Attack allowed people to use Strength for attack rolls instead of Dexterity. This allowed tyrant lizard totem Lunars to show up as a T-Rex and roll 20+ dice for their attacks without spending a mote.
Post-2.5, anything that says "that do not count as dice added by Charms" has a huge sticker reading BE CAREFUL WITH THIS on it. Also, anything intended for Essence 6+ was skipped entirely for the errata, since it was already a Herculean tasknote appropriately enough, given Exalted's classical-mythology trappings, meaning that post Essence 6 things are still horribly broken. Naturally, almost everything that involves the Sidereal Martial Arts is post-E6.
Character creation can make or break you, due to the use of flat costs while most of the advancement table uses (previous level of trait x multiplier). Take two identical Dawn Castes. Have one buy his physical attributes at 5/5/1 and the other at 3/5/3. The first will spend 40xp to get to 5/5/5. The second will pay 56. That's three, maybe four sessions of play ahead, and for only one small part of chargen. Repeat that kind of thing in every section - buy your Infernal eight Charms in a non-favoured Yozi for 16xp free, that kind of thing - and you can end up with one player hit very hard with Can't Catch Up.
Rifts is a game where everyone is a Game Breaker, and needs to be in order to survive the Nintendo Hard combat, but there's one O.C.C. that surpasses even the most broken Juicer or Crazy Hero. Glitter Boy. A character who gets a several million creditmech suit with around 700+ M.D.C. (Mega-Damage-Capacity). A normal character's armor has about 45-100 M.D.C. (To put this in perspective, 3 MD is enough to tear a car in half, and can kill a human several times over), and has a BFG that can inflict up to 100 M.D.C. or more in a single shot. A Glitter Boy can, with a little luck, survive a nuclear explosion. What's the drawback for all this power? The character levels a little slowly, and they have to get out of their mech for a few minutes a day to prevent atrophy.
Magic users can be seriously broken as well; most notable the Ley Line Walker, who starts out with a huge amount of mana/sp, and some of the most powerful magic abilities in the game. And if one is lucky enough to roll good Psionic powers, One-Man Army time. A properly built LLW is capable of withstanding a direct nuke hit by 5th level, and dealing out almost as much damage. And that's before adding insane stuff from magic-heavy expansions like Worldbook: Atlantis.
No magic users will ever be without the most broken spell in the game, Carpet of Adhesion; a 3rd or 4th level spell that is ludicriously powerful, able to glue down and glue together literally ''anything', immobilizing most enemies and turning them to sitting ducks. (To make it worse, this spell is available to some of magic user classes at first level.)
One of the classic examples is the Godling RCC from "Conversion Book 2: Pantheons of the Megaverse". In that you can combine all the useful special abilities of three core classes, superhuman strength, endurance, and regeneration, a 100,000-year lifespan, and some nifty utility powers such as darkvision, seeing the invisible, etc., all for the price of... it's an allowable starting character class, actually.
Then there is the Cosmo Knight from the Phase World sourcebook, who not only is immensely powerful (they're designed to take on starships), but can be combined with just about any other race in the game.
Both the Godling and the Cosmo Knight were created by C.J. Carella, who is quite possibly the Biggest Munchkin Ever.
CJ Carella should have his own section, the man is/was a human Game Breaker. South America 2 has what is arguably the worst example of broken munchkinism. There is a psychic character class in there called the Gizmoteer. One of his powers is the ability to convert any energy weapon so that it runs on psychic energy instead of energy clips. The cost to recharge said weapon is equal to the weapon's payload. The very same book features a gun known as the Anti-Tank Rifle, a very high powered gun (like, it does more than the Glitter Boy BFG mentioned above) designed for armies to give infantry troops a chance against tanks. The drawback of the weapon is that it drains the entire energy clip in one shot, giving the weapon a payload of one. How munchkins can combine these elements to their advantage is left as an exercise for the student.
And let's not get into the stuff you can come up with when you mix sourcebooks and even other Palladium RPGs. One horrific example is the ZentraediTitanJuicerMurder-Wraith. For the uninitiated, that's a fifty-plus-foot giant zombie with thousands of MDC that can only be harmed by magic or silver weapons. Good luck getting a GM that will allow it to happen, but it's perfectly game-legal. Yet again, C.J Carella was responsible for Titan Juicers and Murder Wraiths.
Stun in D20 Star Wars Revised is somewhere between That One Rule and a Game Breaker. If you hit with a stun attack, your enemy must save or be helpless, losing all dexterity, granting a +2 to hit to all attackers, and drops what they are holding for a few turns of combat. If they do save, it happens anyway for one round. Again, this is for every hit, so a party can simply tie up a single, powerful enemy, regardless of size (think rancor) and whittle it down at virtually no risk to themselves. Even if the enemy breaks the loop because all the party members using stun weapons miss (unlikely), they have to take move actions to get their weapons back into their hands, allowing maybe an attack or two before the Cycle of Hurting continues. Do not do this to your players, even as a joke.
Another big gamebreaker was one ability of the Elite Trooper Prestige Class, called 'Deadly Strike'. To qualify for the class at the earliest opportunity, one had to be a sixth level Soldier, then gain nine levels in the Prestige Class. Hard to get? Possibly. The benefit for your patience and hard work? The character in question makes a full-round action to perform a single attack, that deals maximum possible damage regardless of a critical hit. This attack has a doubled critical threat range, and gains a plus four to hit. This is coupled with the character's already high plus fifteen to hit from base attack, plus whatever dex bonus they may have, plus any other bonuses, feats, or special abilities to boot! What does this all add up to? On a crit, even with a measly blaster pistol, anyone getting hit dies, and the odds are that the average to-hit bonus is going to be twenty-five before rolling the d20. Couple this with a blaster cannon, the resident energy BFG, and a few good critical hits, and this character has a decent chance of taking out anything less than a frigate in orbit, by himself, from the ground, in roughly two minutes. Any starfighter will be dust in roughly three to five rounds, long before the pilot can even see the tiny speck down on the ground blasting at it. A round being six seconds long, that amounts to eighteen to thirty seconds, per ship.
SenZar seems to hate the gamemaster with a passion. The "status" power increases a player character's starting money from 1,000 Stars to 1,000,000, in a game with a comically broken artificing system. Proper munchkinisation can result in a player character starting with an armour value of 100, and being armed with a weapon which has a +10 attack bonus, causes an automatic 300 points of damage that will not heal short of 8th Order Magic while healing you for every point it deals, and forces any human you hit with it to make a power save or instantly die. SenZar is probably the only game where a starting character can be armed with a weapon able to kill a normal player character 20 or 30 times over.
While FATAL is a terrible system, it has one spectacular Game Breaker. Your starting level, instead of being 1 like any sensible game, is the square root of the number of years you've been following your profession. Now, this means that a character who has spent 400 years at their job is maximum level from the get-go. Dwarves have their age rolled on 1d1000, and start work before 200. There's also damage XP, which is awarded per class that gets damage XP - so, if you have a few levels in three classes that gain damage XP, you can level up three times faster than someone playing a pure class. The only counterbalance? The assumed Killer Game Master, and considering your GM is likely drinking heavily in an effort to forget some of the things in the rulebook...
In addition, playing a large race and raping enemies in the ear is absurdly easier and more lethal than attacking them normally. Or So I Heard.
Just-as-stupid RPG Racial Holy War (yes, seriously) is broken anyway, but even if fearsome amounts of alcohol and inbreeding have convinced you to actually jury-rig the rules into a playable state, you'll still be left with the hideously broken Athlete player class. See, Athletes get an additional 10 hitpoints per level, since the ability of an experienced athlete to ignore a chainsaw to the head or anti-tank weapon is well known.
Even worse is the Hero class which gives a substantial boost to the Heroism stat and makes all Rouse checks automatically succeed. Because the Morale Mechanic works by adding the whole group's Heroism together for defense and Intimidation for attack and Rouse checks add a set amount to both stats for EACH character based on the Hero's ranks in Rouse, this means that it's pretty much impossible for the party to be intimidated by opponents and will almost always make enemies run in panic. And fleeing opponents can't fight back. And give the party free turns to shoot at them. Worst of all, since multiple Heroes' Rouse checks can stack with each other this means this trick can be pulled at character creation.
Synnibar, full stop. It is fairly reasonable for a party of five people with a decent starting sum and stats rolls to have every PC have 50,000 Life Points, shotguns loaded with Lubricated Pelleum Steel slugs, and be able to attack three times per segment, twice.
A half-pound sling ball of Pelleum can be purchased for nearly 1/200th of the price. After spending the starting funds, the players can have a 100-foot armor-plated pirate ship that could shrug off nuclear bombardment with armor-piercing chainguns and rocket launchers to fire back.
The designers of the superhero RPG Wild Talents freely admit that their (fairly generic) powers-creation system can be easily abused if players are so inclined. The 2nd Edition rulebook even comes with a free example describing how to build a power that will allow the character who has it to extinguish the sun...
The first edition of the Legend of the Five Rings RPG had quite a few gamebreakers. One of the most infamous was a joint grip maneuver from the "Mizu-do" unarmed combat style. A successful roll could disarm and incapacitate the target. Doesn't sound too bad, except that the target's abilities had almost no effect on the easy-to-perform maneuver. As a result, a starting character with fairly normal stats (Agility 3, Mizu-do 3) would have about a 50% chance of disarming some of the greatest swordsmen in the Emerald Empire.
You also get some of the crazies stuff with the Kakita Artisans, who were both underrated and overpowered./tg/ archiveSFW writeup.
Acting Rank 3: "At this rank, the dramatist has gained the ability to physically alter their entire body, so that the dramatist can assume the form of animals. The forms which the actor chooses to become may not exceed the mass of a heavy war horse, and no items (including clothes or weapons) change with the Artisan."
4th Edition has the Asako Henshin, who are simultaneously broken in both directions. At first rank, they get an ability that lets them raise or lower anybody's traits of a certain ring, and it lasts for a very long time even early on. So with a simple action, an Asako Henshin can render trained courtiers into gibbering idiots, out-wrestle a Crab, or out-stealth a ninja. However, the rest of the class is broken in the "unplayable" way, with rank 2-5 abilities being mutually exclusive, being conditional at best, and the class lacks the staple 'can make attacks as a simple action instead of a complex action' feature at higher levels, instead getting a watered-down version at rank 5.
In Eon, you can create an extremely lethal fire spell that makes any one target within 30 meters burst into flame and keep burning for 1 minute, dealing constant damage to everything within 1 meter radius (which means basically the victims entire body). It's a 3rd level spell, but it deals more damage than your standard 5th level spell (and in this game, that's a pretty big leap in difficulty to pull of). So what does it take to craft this spell? A decent score in fire/heat/chaos magic, an average score in the skill Transform Magic, and two different magical effects. And if you up the level of the spell by a tidbit and add a certain third effect, the fireball doesn't go out until the caster says so.
On the other hand, it does have one weakness. Casting the spell requires five rolls on three different skills, and failing any of those rolls means the spell goes of in its unfinished state and the caster has to start over. Of course, this means that if the caster fails on any of the last two roll, the fireball will manifest directly in the palm of the caster. And when a fire with a 1 meter radius manifests with its center right in your hand, yeah you can guess the consequences.
The witch hex misfortune. If the enemy fails their save, then for the next round, they roll twice for any roll using a d20 (which includes attack rolls, skill checks, and saving throws), and take the lower result. Fortunately, it only lasts a round, and you can only use the hex on a given target once per day. However, another witch hex, cackle, uses a move actionnote players get one move action per round (normally used to move), and one standard action (normally used to attack or cast a spell) to extend the duration of most witch hexes by another round. If you can get them with misfortune, and keep cackling, you will have rendered that opponent effectively useless. And since cackle is a move action, you can then tag another one of his buddies each round. Oh, and this build is easy to pull off at first level - just take the feat "Extra Hex".
The Synthesist archetype for the Summoner allows the Summoner (a stereotypical Squishy Wizard) to whistle up a tank-like monster and meld with it to assume the monster's physical stats (making them close to invulnerable) and spell-like abilities, without sacrificing either their own spell-casting abilities or any of their magical items except for armor (which is useless to them anyway). This archetype breaks the game so thoroughly that it's actually been banned from official play, despite having been published in an official Paizo sourcebook in the first place.
In Black Crusade, players can start the game with items of certain rarity (each item has a rarity modified by craftmanship rating and quantity).You can abuse the system to for example start with 1 000 000 poorly trained slaves carrying shitty lasguns. The true gamebreaker comes from the fact that the Heretek class could start the game with 100 of the "mechanicus assimilation" cybernetic upgrades (Hereteks count the upgrade as being more common than other classes, so it only works for them). Said upgrade gives you the "machine" trait, or if you already have it, +1 to the trait and nowhere does it state that there is an upper limit on how many times you can take it. Each level of machine gives you +1 armour, so you can start the game with 100 armour. For comparison, Space MarinePowered Armour has 8 armour (10 on the chestplate if it has the reinforced armour subsystem).
Tabletop RPGs in general can be broken by some strategies that exploit the human nature of the game. These differ from rules-based Game Breakers in that they generally cannot be prevented by GMs except by abandoning the game. For example, in many games the player group can bypass any problem by simply falling silent and waiting for the GM to prompt them through.
In Nobilis, reality is written in a language of flowers. "Flowers" is technically an available Estate. This would create nigh-omnipotence even by the standards of a game where shooting down the sun is considered a fun afternoon.