If your Gambling Skill is at 100% or higher, you almost can`t lose at roulette if you keep placing low bets (about 2$). All you need to do is to hold down the hotkey '1' in the dialogue at the table and wait until you're in the millions. Since everyone except the casinos have limited resources, the whole wasteland economy is somewhat broken.
Even with a pitiful Barter skill level, other people's goods will be worth substantially less than yours. Thus, with a bit of swapping back and forth you can take everything a person is willing to sell you for free. Later games fixed this by jacking up the merchants' selling prices so that even with a maxed barter skill you still pay through the nose for items. However in all games it's possible to shoot the merchant in the face and take all their items for free - sometimes without even being attacked by guards for doing so!
The perk you gain after winning the New Reno boxing tournament reduces normal damage (anything except laser, plasma, fire, explosives, electrical and EMP) by 12 points, which adds to any armor you wear. The calculation is made for each bullet (you can get hit without armor by a minigun blast for no damage), and the only endgame enemies who use laser or plasma are non-military personnel (low HP and no armor) and the end boss.
Abilities that reduce the AP cost of attacks are seriously unbalanced. There is a trait that reduces the AP cost of all attacks by 1, but prevents the character from making aimed attacks. Combine this with perks that also reduce attack AP cost, and by the time you're around level ten, turbo plasma rifle shots cost 2 AP, and super sledge attacks cost just 1. With high agility you can do 200+ damage per turn with no special preparation, which is enough to kill everything but a few bosses in one turn, or shred groups of super mutants.
The Bozar in Fallout 2 has the power of a minigun, the accuracy of an assault rifle, and an ammo type which is cheap to purchase, light-weight, with -20% Armour Class & damage modifier (means the target is more likely to get hit and take more damage) and sold in bulk just about everywhere. This makes it probably the ultimate weapon in-game. A group of shop guards you can meet fairly early on have the gun conveniently unequipped in their inventory. All of them are unusually easy to steal from, even with no points in the Steal skill. Commandeer two of these guns and stick them on a character with a decent skill in Big Guns and you have more than enough firepower to last throughout the rest of the game.
Also in Fallout 2, with a bit of saving and luck you can run straight to an Navarro base, which contains the second best armor in the game, for free. And you don't even need to kill anyone... Since it gives a +4 strength bonus, this is completely ridiculous.
Not to mention all the lockers around filled with the good stuff and insane (at least for early game) amound of experience granted for quests around the base. Navarro Run made as the first thing after leaving Arroyo can grant you at least 5 levels, second best armour (the best one is in The Very Definitely Final Dungeon), more powerful weapons, ammo and equipment than you can carry and all you have to do is go there. Optionally you can also kill (without any repercussions) resident Mad Scientist in sound-proofed room, which gives you access to even more exp and one of the best NPCs. After Navarro Run the game is so broken that all the early quests are not only hardly profitable, but simply boring.
By knowing where to look and a small ammount of reloading, a character can go from 6 points of luck to 10. Combine this with Finess and you get a total critical chance that will likely exceed 20%. Add in a P90 (every bullet can score a critical, every critical will have a HIGH chance to instantly kill a target) and the game is over barring a few more hours of mouse clicking. Being aware of the ways to boost statistics in this game also means you can get 10 ability points in EVERY SKILL when factoring in item bonuses.
As in Fallout 2, you can raise your stats during the gameplay by 19 points like this:
Strength by 6
Perception by 2
Endurance by 1
Charisma by 3
Intelligence by 3
Agility by 1
Luck by 3
Speaking of statistics, a player can have one companion for every 2 point of charisma rounded down. The check for this is based on your CURRENT charisma score instead of your actual one. This means that by tripping on mentats, a character so dumb he cannot normally understand human speech can have a loyal following of five lethally powerful companions who fill out all his dump stats and leave him with barely enough living enemies at the end of the first combat round of any encounter to get a punch in.
The friendly and intelligent Super Mutant Fawkes, whom you can rescue in the main questline. Later, he can team up with you if you have good Karma. He is Nigh Invulnerable, wields an incredibly powerful gatlinglaser, and he steals so many kills that most players have to fire him until and unless they've hit the level cap.
The Tesla Cannon gained at the end of Broken Steel uses very common ammo and is (almost) a guaranteed 1-hit-kill, with area damage in case you miss.
The Chinese Stealth Armor from Operation Anchorage makes you nigh invincible, provided you have decent stealth (about 80). It allows you to sneak up to an enemy, from the front, set them on fire with a flaming sword, be pushed around by them, shoot them with little darts and plant explosives on them in full daylight without ever being detected. Thanks to the automatic critical when attacking undetected, most foes go down from the first hit. Got detected anyway? Retreat, wait a few seconds, be hidden again. Add to this that nobody gets alarmed by their friends suddenly going up in a blaze (more criticals), and you have the ultimate armor.
Ontop of the Chinese Stealth Armor's greatness, you could put all the different variants of hats on while wearing the armor. Getting the DR of a light tank.
The Grim Reaper's Sprint perk restores all AP if you kill an enemy while using VATS. Now consider that with decent stats it's ridiculously easy to kill at least one enemy in each VATS cycle; also consider that while VATS lasts you're effectively invulnerable. Keep hitting the VATS key as you exit it, and you'll slaughter every enemy in range while scarcely receiving any damage yourself.
There's a setup that turns every single standard attack into a critical hit. Deathclaw Gauntlets do 20 damage per hit, a critical hit gives an additional 30 damage. As previously mentioned, they ignore armor, so they'll always do the full critical damage every single hit.
Several of the unique items that comes from the Monty Haul that is Operation: Anchorage:
The Winterized T51b Power Armor. Not the strongest armor in the game, but the developers accidentally put in the nigh-indestrucible simulation version - odds are it'll never drop a single point of DR in an entire playthrough.
The Chinese Stealth Armor. Repairable with Recon Armor and gives a permanent stealth field while sneaking.
The Gauss Rifle. Essentially an Energy Weapons sniper rifle, it has high damage, uses the common microfusion cells, and knocks down enemies on critical hits. Oh, and it has a critical multiplier of five.
It's also worth noting that a particularly sneaky player can place a corpse into the VR pod (in a seated position, which can be tricky to arrange), allowing them to place all their virtual equipment into the corpse's inventory before the game takes it away as you're waking up. The game will search your inventory for virtual items just a few seconds later and find nothing, allowing you to loot the corpse for all your invincible gear. Using this trick along with shooting and stealing Jing Wei's Shocksword out of his hand gets you an unbreakable set of armor (with some items you can't get any other way) and Shocksword which does electricity damage on hit.
The steel ingot rewards from The Pitt are several powerful unique items, but two are worth special mention:
The Steel Knuckles, having the lowest AP cost of any weapon in the game. Combined with Paralyzing Palm, even Deathclaws are helpless in melee.
The Perforator assault rifle beats out every other assault rifle in accuracy, comes with a scope to boot, and is silenced, allowing you to punch holes in enemies from a distance.
From a simple side-quest (or Sequence Breaking) in Point Lookout, you can get the Backwater Rifle, a unique lever-action rifle. While Lincoln's Repeater barely beats it in terms of standard damage and clip capacity, the Backwater Rifle uses the very common 10mm ammo as opposed to .44 magnum and has a critical multiplier of five as opposed to two.
Alien epoxy from Mothership Zeta. It restores a fixed percentage of the durability on your equipped weapon based on your Repair skill - even weapons that can only be repaired by merchants. There are over a hundred throughout the Mothership and you can get an infinite amount after the expansion questline is completed.
Even one of the basic alien weapons is a Game Breaker: the Alien Disintegrator. It packs a punch while having a clip size of 100 shots and literally reloads with a mere press of a button. You'll have thousands of shots if you save up throughout the expansion.
Fallout New Vegas
The game is chock-full of Game Breaker weapons and armor that can make quests and enemy encounters a breeze, even from the start of the game.
Shotgun Slug ammo. Normally, shotguns do a fair amount of damage divided into several small bullets (around 7). This means that, once you start facing armored opponents, your shots won't do diddly. However, slugs condense that damage into a singe shot that does the same total amount of damage. Even better, with the perk Shotgun Surgeon, your shots ignore 10 DT, meaning that anything wearing light armor may as well be naked. The higher level shotguns, in particular, the hunting shotgun and it's unique variant, Dinner Bell, can take out most any human target (excluding Lanius) with only a couple of shots at most. With Gun Runners Arsenal, you can buy Pulse Slugs, which do less damage, but are extremely damaging to robots and power armor. Combine this with Center Of Mass and Bloody Mess, and you can reduce enemies to a pile of bloody chunks that are no longer identifiable as human remains.
From the Dead Money DLC:
The lovely little gem known as the Holorifle. This is a scoped energy rifle that is, with Max Charge cells, outdone only by the Gauss rifles, but unlike Gauss rifles, a shot only requires one round of ammo, not four or five. Plus, it can be upgraded to do more damage, with reduced spread and improved condition. It also performs a damage over time effect to any enemy it hits. And while it can only be repaired by NPC's or weapon repair kits, at 100% condition, standard ammo causes no degradation. Use Overcharge or Max charge, though, and it takes damage. More importantly, it isn't affected by the Commando perk, or any of the energy weapons perks. While this sounds bad at first, this means that you DON'T need to take these perks if you're going to be a holorifle based character, freeing up several perks for character growth that you otherwise would not have available. The best part? You don't have to hunt for this weapon, you receive it at the start of Dead Money. The only thing you have to hunt for are the mods, two of which are located in areas you have to go to complete the storyline.
Any player with a decent Luck stat can utterly break the game thanks to the Sierra Madre casino. After you've earned enough chips, one of the rewards will be chip vouchers which can be redeemed at a vending machine. Once you get back to the Mojave, three vouchers will be delivered to the safe in the waiting room every three days, for a total of 1100 chips. Using the vending machine in the room, you can convert these chips into anything on the menu, particularly Stimpaks and Weapon Repair kits. Congratulations, you now have infinite healing and weapon repair. To make it clearer, Stimpaks are 25 chips each, and Weapon Repair packs are 20. For those of you not wanting to do the maths: 44 Stimpaks. 55 Repair Kits. For free. Per three days.
The extremely heavy but valuable gold bars. Using numerous weight-reducing tricks, a player can, unencumbered, carry about 5-7 total, which is more like 1 or 2 if you're properly armed. They're supposed to represent letting go of greed (unlike Elijah, who will stop at nothing to get inside the vault). Though it takes some cleverness, it is possible to carry out the entire stash with time to spare by exploiting scripted events. Getting away with all the gold will net you 389,943 caps - it's impossible to find enough vendors in the entire game (DLC's and all) who have that many collective caps, let alone enough to buy a single bar off the player. The weight to value ratio is also extremely low compared to a lot of the nicer weapons, though it is certainly convenient.
A Glitch in the x-box 360 and ps3 version of the games gives the aforementioned complimentary vouchers awarded to the player at regular intervals a surprising use. When dropped the holotapes will float in the air, allowing a player who stocks up enough of them to build a chain of stairs to get to just about anywhere. It is popular to use mods to get the same effect in the Pc.
From the Lonesome Road DLC:
ED-E is a deliberate Game Breaker given to you right at the start of the mission. Most notably, after collecting two circuit boards (one found in the same complex where ED-E was activated), you will receive the option to have your weapon repaired by 25% once a day (thereby saving you thousands upon thousands of caps in repair fees), and you'll get free ammo every day (which, depending on your Speech or Repair skill, will net you Energy/Microfusion cells, flamer fuel or satchel charges). You'll never have to worry about weapon degradation or running out of ammo for the duration of the DLC. The best part, however, is that all these benefits transfer over to the main game's ED-E - have fun!
The best rocket launcher in the game, Red Glare, is more or less handed to you a third of the way through your quest, and three mods for it are sold at every Commissary in the Divide. If you've been saving your caps (or if you decide to abuse the Commissary's replenish stash of caps), you can get all three mods as soon as you get it, and use the fully-upgraded auto launcher with the best zoom (4.35x) in the game immediately.
Turbo, a rare chem which creates a "bullet-time" effect that slows down everything except for the player, allowing you to dodge any attack with minimal effort. It's not a game breaker by itself because the duration is normally very short, but with a certain combination of perks it is possible to get its duration up to a full 30 seconds (a full minute with one of the traits found on DLC)—more than enough for you to win any encounter with a single dose. The other balancing factor is that it is extremely rare, but this too can be overcome if you find the recipe, because the individual components are fairly common.
Turbo's Game Breaker potential is limited by its aforementioned rareness. The Implant GRX perk can be taken at level 30 and has the exact same effect as a dose of Turbo, albeit with a shorter duration. However, with the previously mentioned drug extending perks a single shot of GRX lasts 20-30 seconds, depending if you have rank one or two of the perk, more than enough to kill anything in the game, and if somehow you can't finish a fight up in time, feel free to take another FOUR to NINE doses (rank 1 or 2 respectively). That reset daily. Oh, and did I mention it's impossible to become addicted to it. It stays with you in Dead Money. The only real down side to basically being the flash with a gun is an 8 endurance entry fee.
Debatably an Infinity+1 Sword, PEW-PEW is easy to acquire fairly early in the game with a bit of knowledge and consuming every bottle of Sarsaparilla you come across. Sure, it eats ammo like a starving man devours fresh bread, and yeah it only can shoot two rounds before reloading. With this price however, comes an extremely easy to repair, improved holdout weapon, with insanely common ammo, that does some of the highest damage per shot, and with one of the highest crit multipliers and crit damages in the game. Even someone with no skill in energy weapons whatsoever can drop the highest level death claws in a few shots. Someone with a reasonably optimized energy weapons build, well... let's just say that those two cons I pointed out above no longer matter.
For those who don't mind outright glitches, getting between 33K and 34K casino chip from any one casino and then dropping them causes the computer to... go funny in the head, causing the dropped chips to overflow and read as negative. Picking the chips up again adds them to your inventory...only they can't be removed.Even by cashing them in.
The "And Stay Back!" perk gives every projectile from a shotgun a 10% chance of knocking them down. Since standard buckshot is 7 pellets, this gives meat shots about a 50% chance (14 pellets and about a 75% chance using the double-barreled Sawed-off shotgun or Big Boomer) of rendering any enemy but Ulysses, Gaius Magnus, or Colonel Royez helpless for several seconds. Since you can still knock them down when they're in the middle of getting up, forcing them to start over, you're pretty much guaranteed to stun lock any enemy that you can engage at close range.
The YCS 186 Gauss Rifle. Its accuracy makes it very easy to get headshots from such a distance sneak attacks can be easily made even with a very poor Sneak skill. It's already strong enough to kill most human enemies without a crit; long-distance sniping can one-hit kill against almost anything. You can find it for free pretty much as soon as you reach New Vegas, provided you know where to look.
Having Boone (enemy targets highlighted for you when you look down your sights) and ED-E (enemies show up on radar from the maximum distance possible) with you makes long-range sniping a breeze, especially if you have a suppressed sniper rifle like the Ratslayer.
A surprising gamebreaker is the humble cattle prod. While it does pitiful damage against anything, it still stuns nearly every enemy in 2 or 3 hits, leaving them at your mercy if you repeatedly restore the stun effect. You could literally poke them to death. This includes Death Claws, Giant Rad Scorpion Queens, Cazadores, or even Securitrons. If enemies get too close, this is basically the perfect emergency weapon.
Sneak attack criticals are absolutely devastating, especially combined with a headshot. That's why weapons like the Ratslayer, which has weak stats, can be gamebreakers. For reference just how low the Ratslayer's stats are, the Silenced .22 pistol, the absolute weakest pistol in the entire game, has slightly higher DPS than the Ratslayer. Only three pistols (.22 pistol, 9mm, and Maria, the unique version of the 9mm) do less damage per shot. Despite this, it becomes devastating when used with sneak attack criticals.
Jury Rigging is a pretty big game breaker. You can repair anything with anything even remotely similar to it, so you can fully repair that Hunting Shotgun with a few cheap Single Shotguns and then sell it for tons of caps. It requires 90 repair to unlock, but that is totally worth it for the massive benefits you get.
The compliance regulator from Honest Hearts, does almost no damage, but every time it lands a crit it will stun the target for several second making them easy to pick off with a more powerful weapon. It also has an amazing fire rate so it's easy to spam hits at a distant target and land at least one crit before it reaches you and uses the very easy to find SEC's for ammo. The best part is that nothing in the game is immune to the stun, not even any of the end game/DLC bosses which are normally immune to being knocked down. If you crit it, it will fall over stunned for quite some time.
For the game-within-a-game, Caravan is trivially easy to win once you've built up enough even-numbered cards and face cards. By stacking the deck with 6, 8, 10, Jack, and King cards, you can not only get a solid 26 on every caravan within a few moves each, but can also easily sabotage your opponent.
Jury Rigging lets you repair one weapon with any other weapon in the same of a few groups (i.e. one-handed guns, two-handed melee, etc.). Guns in the same group are often of wildly varying value—for instance, an anti-materiel rifle (5600 caps) can be repaired with a BB gun (36 caps) or Varmint rifle (75 caps). Since the repaired item will have a condition at least as good as the one it's repaired with, you can repair a very expensive item from any condition to full using one of a very cheap item that is in perfect condition (which are easy to find in poor condition and cheap to have repaired by NPCs). This effectively negates any effect condition will have one equipment you use, with a side-effect of destroying the game's economy: you can makes thousands by just buying all of a merchant's high-tier but damaged items, repairing them, and selling them back for a massive profit. This doesn't have such a huge effect in the base game, because by the time you reach Jury Rigging's level requirement there's nothing money will really get you, but Gun Runner's Arsenal adds loads of unique, powerful, and expensive weapons that you can only get from merchants—and they're often available extremely early in the game, just prohibitively expensive.
The Tarantula frequency sonic emitter from Old World Bues is a pretty decent weapon on all its own, does good base damage, uses common ammo, sets enemies on fire with a critical hit. However a game glitch sometimes when scoring a crit the critical kill animation will play even though the target is still very much alive. Since the critical kill animation consists of exploding the enemies limbs off, this results in a chance at an instant kill.