The humble Pistol was the weapon of choice for most people, even beyond several of the weapons found later in the game. It had the best accuracy, damage, rate of fire and was available from the beginning of the game. With a little tweaking, you could turn it into a good long range killing machine (without bothering to use the Sniper Rifle). The pistol's Marksman ability, at maximum, will also out-shoot Assault Rifles easily - more rounds, more damage, less heat and more accuracy. With the Infiltrator class, specializing in Commando, as well as a Medical Exoskeleton, it can speed up the recharge on Marksman to the point where you can have the skill enabled permanently.
Now combine Pistol's Marksman with the Immunity ability. You can basically stand still right in front of a pack of six enemies who all have guns blazing on you and methodically take them all down one by one before Immunity wears out. This will work on any game difficulty! The only problem with this is the presence of an enemy biotic who can knock you down on the floor repeatedly, but there is only two or three of those specific instances in the whole game.
Shotguns, fullstop. ME1 shotguns do have very tight pellet groupings that grant considerable range. With the right shotgun stats and equipment, you have a nonscoped sniper rifle in your hands. Add to that high force upon hits and the ability to equip shotguns with specialized ammunition that increases impact force even further and the only thing you can't tie down to the ground are Krogan. And those still die fast enough, even on Insanity if you can hit them before they cast Immunity. If they managed to, well, biotics are instant win abilities.
An Adept's skills, when set up properly, lasted longer than it took for them to recharge. On top of that, they have the ability to damage anything in a Stasis field, which can't fight back. This ability works on the final boss.
Adrenaline Rush. Unlike the later games, each power in ME1 had its own cooldown, independent of all the others. What Adrenaline Rush does is reset the cooldowns of all your powers so you can use them again instantly. In the hands of a Vanguard, this essentially amounts to dual-casting Lift, Throw, and Barrier, with a side of Marksman/Carnage for good measure. And by the time all those run out, you'll probably be ready for another Adrenaline Rush. Oh, and since you've got a bio-amp anyway, Vanguards are ideal for using a biotic bonus power like Singularity for even more chaos. And in case you're worried that tech powers were left out of the fun, Garrus also packs Adrenaline Rush for all your rapid-fire-Overload/Sabotage needs. Enjoy.
Soldiers and Infiltrators both could get Master Immunity and a specialization to reduce its recharge time to be identical to its duration. This ability made the player virtually invincible and could be reused as soon as it wore off. It completely negated the need for cover, which is supposed to be a major defensive component. It also negated the benefits of taking defensive bonus talents, which were pretty logical choices for a Soldier if you didn't realize how effective Master Immunity was.
The Spectre Master weapons, gained by amassing a million credits and buying them from the C-Sec/Normandy requisitions officer (and can be done very early on, if you save enough). Every other gun pales in comparison.
The Mako can be this at times, just about every outside fight is meant to be fought from within the Mako, but if you manage to find one that isn't and still got the Mako there? Well then you have what's essentially a sniper rifle with the ability to kill anything meant to be fought from the ground in one shot. Goodbye difficulty! Although this does significantly decrease the XP received from kills, nothing prevents you from damaging enemies down to a sliver of health and then Cherry Tapping an enemy to death- which you could also do with any fight you use the Mako in, allowing you to net more xp than any fight in the Mako was intended to give you.
The Bastion specialization for Adepts and Sentinels. Generally being Squishy Wizards, if you did the Luna mission early enough and saved some of your upgrade points, once you get the extra options opened by the Prestige Class you can add a large boost to your Barrier's defense capability and make it regenerate 40 of your shields per second as long as it is active, adding up with duration and shielding bonuses to the point where you can keep laying down a barrier at the start of every firefight and never worry about using medigel again, especially if you use a Medical Exoskeleton. And with a few more points into Bastion, you gain the ability to deal damage to enemies immobilized by Stasis, making the Final Boss an absolute breeze.
Mass Effect 2
The Mattock Assault Rifle for the soldier. It deals ungodly damage in Adrenaline Rush note Adrenaline Rush drastically boosts damage while slowing time, and weapon fire rate slows proportionally. The Mattock, however, has no built-in limit on how quickly you can pull the trigger., is extremely accurate, and is available from the start of the game.
The M-29 Incisor Sniper Rifle is a DLC weapon that does decent damage when Shepard equips it, and is available from the beginning of the game. Give it to your allies, however, and you can walk through most of the game without firing a shot, especially on Insanity difficulty (and right from the beginning of the game). As this video shows, Zaeed and Garrus will mow down most enemies in three or four shots, while the player can stay behind and play "spectator" as the AI kills everything in the way with massive damage. According to the game coding, squadmates do reduced damage on higher difficulties with most weapons except those obtained through DLC, making the M-29 king of the hill.
Mass Effect 3
Vanguards have become field-wipers thanks to their new ability, Nova. Nova is normally a Death or Glory Attack because it drains your shields to cause a huge biotic explosion. However, the vanguard staple Biotic Charge regenerates shields, up to 100% capacity with the right upgrade. Should a vanguard equip a light enough weapon, the cooldown between the two can be short enough that a skilled player can jump around blasting any enemy in view over and over again until all that's left is a pasty smear on the wall. And have we mentioned that both Biotic Charge and Nova give the player invulnerability during their duration, making a skilled Vanguard all but invincible?
Note that this doesn't extend to multiplayer, where Vanguards (beside the Krogan) are incredibly squishy, not powerful enough to be a viable Glass Cannon and almost unplayably laggy if not hosting. They are very tough to play well and even then there are better classes.
If the player is hosting, however, a certain trick you can perform when you use the Nova note The game grants about a second of immunity to any form of damage whatsoever, which you can exploit by canceling the Nova by, for example, rolling to the side or performing a quick melee attack. Provided you don't run into enemies that can instantly kill you or stagger you, you could walk across a field of Cerberus turrets and come out none the worse for wear by abusing this. turns you into an unstoppable killing machine with some practice. Slap a powerful, yet light enough gun on the human Vanguard and you won't need teammates.
Vanguards also have access to the Shockwave ability. These stumble and harm even the toughest of enemies and can be fired around corners or through walls. If you can max it out for range and cooldown a Vanguard becomes almost unstoppable.
Vanguards also have access to the Incendiary Ammo skill, explained below. It's interesting to note that the skill only applies the extra damage to Health and Armor, but the Nova skill above can get a massive damage boost to Shields and Barriers. Vanguards have all their bases covered with game-breaking abilities.
Now that Overload works against both regular shields and biotic barriers, it's surpassed Warp as the go-to anti-defense power. In addition, it's later evolutions can make it jump from target to target chain-lightning style, as well as impart a neural shock effect. Put all these together, and you've got multi-target, anti-shields, anti-barrier, and stun, all in one power.
Likewise, the Energy Drain power has also gotten a similar boost. It can't chain like Overload, but simply making it usable against barriers means that no matter whether you're fighting husks, Cerberus, or geth, there's at least one enemy type available to drain from. This is particularly useful for Infiltrators, since they don't get Overload by default, and the main drawback of Tactical Cloak is that your shields do not recharge while it's active. Energy Drain solves both problems, which is why Salarian Infiltrators (who have Energy Drain) are so prominent in multiplayer.
Incendiary Ammo. The final stage of the skill grants a chance of an explosive burst. The damage of the burst is a set amount of damage (roughly 100 points), unlike previous games where the damage was a percentage of the weapon damage. The upshot? Fast-firing weapons trigger this explosive damage more often. With fast-firing, low-damage weapons this skill can effectively boost damage by +200% while adding an area effect. The Particle Rifle is generally the best weapon to use with this skill, as it has a fast fire rate, can be upgraded with cover penetration, has perfect accuracy, and regenerating ammo. The Geth Pulse Rifle is probably a close second.
This game's version of Stasis has the most potential for game breaking yet. Unlike the first two games, enemies under the effects of Stasis can take damage (though too much damage will break the stasis effect). It also acts as a source power for biotic explosions (which means you can follow up with Warp or Throw for massive damage), it ignores shields and barriers (so Phantoms among others are not immune to it), and a Rank 6 evolution lets it create a bubble that will stun any unarmored enemy that walks into it, essentially making it a multi-target trap like Singularity.
On anything less than Insanity, where the AI becomes smart enough to work around it, Tactical Cloak is this. While the Infiltrator's signature weapon is the sniper rifle, using Tactical Cloak with just about any shotgun, the Carnifex, or the Paladin means you can run around a map free from enemy fire, walk right behind them, shoot them in the back of the head for massive damage, hide behind cover for what might be, depending on your level, 3 seconds and then you can do it all over again.
Flare, a bonus power unlocked upon completing the Omega DLC. It's a biotic power that triggers a powerful explosion with a huge radius. It has a base radius of 6 meters, roughly twice that of any power other than some of the grenades, and can be evolved up to a potential maximum of 10.8 meters. Meanwhile, it inflicts close to or over 1000 points of damage, much better than other offensive powers like Warp, and it can be used to detonate Biotic effects and even has an evolution for increasing the damage, force, and radius of Biotic Explosions. Although it's got the longest cooldown time of any power to date in single player, Shepard can still pretty easily bring it down to six seconds or less by selecting lightweight weapons and gear and bonus power recharge rate boosts. Doing nothing but heading for cover and casting it multiple times is sufficient to win most encounters, since each casting will inflict heavy damage to all large enemies in the radius and instantly kill all mooks.
Oh, and it sets off pre-existing biotic primers, such as Reave, Warp, Singularity, and a few others. Double explosions FTW!
The M8-Avenger is the game's starting rifle, and as such is a Jack of All Stats, with no major weaknesses except being unpredictable at long range, and no major strengths other than being very lightweight. The High Velocity Barrel from the Omega DLC turns the Avenger into a death machine as it ignores 90% of armor and punches through cover like it was made of toilet paper. The reason why the HVB is the perfect match for the Avenger is that the HVB adds a weapon's weight by 50%, but the Avenger is so light that with a few upgrades it practically negates the weight penalty, making it an awesome combination for power-spamming classes. This also works with the M7-Lancer.
The N7 weapons included in the Collector's Edition are all near or at the top of their class, are available from the start of the game, and (with a mod or two) become devastating:
The N7 Crusader Shotgun. It fires a single, accurate, solid slug rather than buckshot. This essentially makes it an unscoped sniper rifle, with comparable stopping power to the single shot sniper rifles...except it's semi-auto.
The N7 Eagle. It's got the accuracy and power of a pistol, and the fire rate of a SMG. Put a scope on it, and you have a full auto Sniper Pistol. Like the Particle Rifle, you can probably take nothing but the Eagle and do just fine. Note that this doesn't apply to multiplayer, where the N7 Eagle is seen as one of the worst guns in the game.
The N7 Valiant sniper rifle. Like the prohibitively expensive Black Widow, it combines a three-shot clip with good stopping power. Unlike the Black Widow, its recoil and reload time are practically nonexistent, making room-clearing a breeze, and it's light enough to keep power recharge high, and cheap enough to upgrade that you'll get it up to level V moments after the first level.
The N7 Hurricane; if you can learn how to handle the prohibitive recoil, it's got more power per shot than any other SMG, and with magazine expansions, can dish out a whole world of pain. It's especially game breaking when employed by the Turian Soldier class in multiplayer with level V heatsink and thermal clip mods. The Turian Soldier's signature skill, Marksman, increases the firing rate and ammo count and decreases the recoil of his guns. In his hands the modified Hurricane becomes a super accurate death machine that never stops firing.
Several of the weapons obtained through DLC packs are ostensibly broken from a damage output standpoint, and most of them can be accessed from the beginning of the game:
At the top of this list should be the Cerberus Harrier, from the Firefight Pack DLC and the multiplayer Rebellion DLC. As of the MP Reckoning expansion, it is the most commonly used weapon in multi-player. Why? It deals great damage, is fully automatic with a high rate of fire, and is only a mid-weight assault rifle. It stands head and shoulders above every other assault rifle, and can be used by a wide variety of classes, save the most power-centric. Its only flaw is a truly horrendous clip size.
The Particle Rifle (from the From Ashes DLC) runs on the same "cooldown" system from the original game, but also uses a beam that gets stronger as the trigger is held down. Not only can the weapon be acquired extremely early (by doing Javik's mission right after Mars), but it can also be augmented like the other weapons with mods. A Particle Rifle with a magazine upgrade and extended barrel will have much more ammo than normal, and will chew through enemy defenses easily, even on Insanity difficulty. Even better, if a Soldier class runs the beam's ammo down to 0 and uses Adrenaline Rush, the weapon's reloading animation (which often takes several seconds) is skipped and the ammo will refill again, saving precious seconds in combat.
The Venom Shotgun from the Groundside Resistance Pack DLC is described, even on the ME wiki, as having all the benefits of a heavy weapon from the previous game, minus the ammo issues. With maxed-out upgrades, an extended barrel and incendiary ammo (which is fairly easy to accomplish early on), the Venom becomes a beast that can one-shot Brutes and Phantoms, and take down Geth Primes, Banshees and Atlases (some of the hardest enemies in the game) in three-four shots. Aside from weight issues, it makes any difficulty up to and including Insanity a complete joke.
The N7 Piranha shotgun (also from Groundside Resistance and the Earth multiplayer pack) has very poor accuracy and a small clip size, but with the right stability upgrades it can do monstrous damage with near-perfect accuracy. To put this in perspective, in single-player, the Level I version of the Pirahna is better than the Level X Katana shotgun (which is also acquired near the beginning of the game).
The Krysae Sniper Rifle (from the Firefight Pack and the Rebellion multiplayer pack) might as well have been called the Krysae Rocket Launcher. Though it can't get headshots, the rounds it fires are explosive and operate on a proximity charge, allowing it to blow up groups of targets with one or two shots each, even on Gold difficulty. With a few damage bonuses even boss-type enemies fall prey to the Krysae's wrath. This gun was the reason that Tactical Cloak and Hunter Mode were nerfed in multiplayer, since they both provided too much synergy with it. And even after being nerfed, it's still in widespread use to this day.
The M-7 Lancer Assault Rifle (from the Citadel and Reckoning DLC) combines the recharging ammo of the Particle Rifle with the power and high rate of fire of the Cerberus Harrier, giving you arguably one of the most powerful weapons in the game. And on top of that, it is also one of the lightest assault rifles in the game, so all but the most power dependent of classes can use it without any problem. The only downside is the slightly less than forgiving recoil which can easily be taken care of with a stability mod.
The M-11 Suppressor Pistol (also from the Citadel and Reckoning DLC) might not have the stopping power of other pistols like the Carnifex or Paladin, but it makes up for it with one of the largest head-shot bonuses in the game. If used with the correct mods (the scope and cranial trauma mods are the two best choices) and enough skill, the Suppressor can reliably kill just about anything except for the heaviest of heavy enemies in two shots or LESS.
If you purchase the Citadel DLC Liara gives you a gift, the M-90 Indra. It's basically a full auto sniper rifle that might not have the punch of, say, the Widow, but add ons and upgrades fix that. Throw in special talents like cloak or the ability to slow down time when aiming and you could take down Harvesters. Unaided.
The N7 Typhoon is the most obscenely powerful weapon in the series. Once it has reached its maximum firing rate, it causes double damage against all types of protections. When used by Shepard or in multiplayer, it's balanced by being extremely heavy and having horrible stability. What breaks the game is that Shepard's squadmates are completely unaffected by weapon weight and have perfect stability no matter what. It is a testament to the power of the Typhoon that even Kaidan and Javik, who need to rely on other squadmates for ammo powers and potentially have no weapon damage bonuses at all, are capable of easily melting the toughest enemies. Ashley's Marksman ability or James' Incendiary Ammo that was mentioned above, break it even more. Some players eventually stopped giving their squadmates Typhoons because the game became too easy.
Infiltrators in general. They benefit from Tactical Cloak's unique cooldown mechanic - should the Tactical Cloak be canceled before it naturally expires, it has a reduced cooldown. You can break cloak early by shooting or using a power, and getting a damage boost from cloak. Normally, you'd want light weapons (which give bonuses to cooldown) to ensure the cooldown for a useful power like Tactical Cloak remains short. However, by breaking cloak immediately after engaging it, you can force its cooldown to be as low as three seconds. This means Infiltrators get an unparalled damage boost to both powers and weapons (most classes only have passive skill trees that benefit one or the other), and can carry the heaviest (and generally most powerful) weapons in the game while still spamming powers freely with Tactical Cloak's damage boosts.
Multiplayer has its share of incredibly broken classes and skills:
The final MP DLC, Reckoning, all but cements the place of Infiltrators as the most powerful class, in the form of the Alliance Infiltration Unit. The AIU has a unique cloak similar to the Turian Ghost's: its final evolution at rank 6 can give a boost to shotgun damage fired from cloak. Powerful, but not game-breaking. It's true power lies in another ability: Repair Matrix. Repair matrix offers the AIU some general buffs (speed boost, damage reduction, and shield regeneration), and most importantly, a free revive when she would be downed. For literally very other character in the game, going down means you either wait for a teammate to revive you (and risk being executed by an enemy or simply bleeding out in the meanwhile), or using a medi-gel (of which you can bring at most 6 per game). Proper application of Repair Matrix means you will never die, because you'll revive instantly. The kicker? Repair Matrix is a grenade-based power. This means you can freely refill at ammo boxes. Because Repair Matrix can have a duration of roughly 20 seconds, you can simply run from ammo box to ammo box, all under the protection of Repair Matrix, and so completely trivialize damage taken and death.
The Asari Huntress is perhaps the most powerful asari class. They have Tactical Cloak, of course, and Dark Channel, a powerful biotic damage-over-time power (previously only available to Javik in single-player and the N7 Fury in multiplayer). These two powers combine for a devastating ability that eats up foes' health. First, the Huntress's Tactical Cloak was released bugged—it only gave damage boosts to melee attacks and powers, not weapons. Rather than wait for a patch to fix the bug, it was decided that the Huntress would be given a unique Tactical Cloak: her Tactical Cloak can give a 120% bonus to general damage (though that still only applies to powers and melee) as opposed to the 80% of other Infiltrators, with a further 40% boost to biotic powers instead of sniper damage. Second, Dark Channel while decently powerful but not exceptional on its own, gets a damage boost from Tactical Cloak for the entirety of its duration. So while your cloak may break right after you use Dark Channel, it keeps that 120% damage boost until it runs out... and if its current target dies before that duration expires, it'll simply jump to a nearby foe. A Dark Channel cast under cloak is capable of killing a Banshee from full health on Gold difficulty, all while the Huntress is running about targeting other foes.
The Drell Assassin Infiltrator, as yet another example of why Infiltrators are often considered the most powerful class. Drell have excellent passive bonuses to power and weapons damage, with a unique speed boost evolution in another skill tree, making them fast and hard-hitting. As an Infiltrator, he also gets Tactical Cloak. And he gets Recon Mine, which highlights all enemies in a rather large radius, making them visible through smoke and even walls, as well as potentially slowing them and making them more vulnerable to damage. The icing on the cake? You can detonate the mine, dealing massive damage to all enemies in range. Recon Mine is only available on the Drell Assassin and the Volus Engineer, which as a support class offers much less damage potential. Its fortunately balanced by the fact that Drell are Glass Cannons, with low base health and shields.
The Geth Inflitrator toting an N7 Piranha is agreed by many to be the best multiplayer character. The already overpowered Piranha loses its spread thanks to accuracy bonuses, becoming viable at range, and its already high damage is amped up by cloak, hunter mode and (optionally) proximity mine debuffs.
The Geth Juggernaut, basically a playable version of the Geth Prime, is the strongest Geth character. It has more health and shields at Level 1 than most classes could possibly get, and all of its powers can be evolved to further increase it's toughness. It also has a heavy melee that stuns non-armored enemies (including Phantoms) and recharges its own shields like Energy Drain. While the Juggernaut is so big that it can't use most cover and moves very slow, its also immune to stuns and insta-kill moves, which makes it possible to take on any of the biggest enemies head-on. A group of Juggernauts is even more devastating, as they can assist each other by stunning enemies, deploying energy shields as cover and turrets that can restore each other's shields. The N7 Destroyer pales in comparison.
The N7 Destroyer Soldier is basically Iron Man brought to the Mass Effect universe. The character is in a big suit of powered armor and is quite powerful. Devastator Mode, even after being nerfed, increases weapon damage, rate of fire and magazine capacity in exchange for losing a bit of movement speed. Additionally, with Devastator Mode active, the Destroyer cannot be stunned. That means that all those overpowered Geth attacks that cause you to stumble will still damage you, but your firing won't be interrupted. Secondly, the Destroyer has the Hawk Missile Launcher. It's an auto-firing missile launcher that can be upgraded in a variety of ways. Its only drawback is that it decreases your max shields. That's a small price to pay for a missile launcher that has an unlimited ammo capacity, doesn't need to be manually locked on or fired and stuns most regular enemies. Finally, the Destroyer has Multi-Frag Grenade, which is pretty good when it comes to grenade powers. All that, though? Not the best part. The best part is that apart from enabling Devastator Mode and the Hawk Missile Launcher at the beginning of a match, the Destroyer never has to worry about cooldown. That means that a Destroyer player can equip the heaviest two weapons he or she wants with no penalty whatsoever. It's no wonder why Bioware nerfed the Destroyer.
The N7 Shadow possesses Shadow Strike, a teleporting backstab that synergises with its cloak and lets it zip around the field like a Vanguard. When set up properly it can inflict massive damage (boosted by both melee, cloak and power attack bonuses) without breaking cloak, possibly twice in a row. The class also has the benefit of cloak (handy for objectives and reviving allies) and a cover-piercing shockwave attack that can set up its own tech bursts and be used in combo with Shadow Strike.
The Targeting VI, an item which will augment headshot damage by 25%, 50%, or 100%, depending on the level. If you can consistently get headshots, you can use this in conjunction with a semi-automatic sniper rifle - say, the Raptor or the Viper. Watch yourself score at the top of matches every time.
The Turian Ghost infiltrator class has amazing synergy with assault rifles, with class passives improving stability and a cloak variant that boosts their damage even more than normal damage-specced cloaks. They combine this with the general utility of cloak, a cloak-boosted overload for stunning and shield-stripping, and Stim Packs, which are deployed instantly like grenades and instantly refill shields (temporarily raising them above max) and give a damage bonus. They can get all this power and survivability and still use heavy weapons without penalty by breaking cloak as soon as it deploys.
The Krogan Battlemaster is what Shepard would be if s/he had four testicles. He finds the concept of guns and keeping distance from a fight quaint, launching into the fray with a biotic hammer that can one shot lesser foes. He gains strength from the ludicrous amounts of enemies he can kill, and has tech armour to replace shields. Which probably won't be needed, he regains shields and health at an ungodly rate.
Power combos are nice enough on their own, but what really broke the difficulty in the single-player was when some observant players discovered the ability to chain different types of power combos. Before patches, it was discovered that using Warp to detonate a Tech Burst did not stop it from priming the target for a Biotic Explosion. Patch 1.04 introduced the ability to keep up repeated Tech Bursts and Fire Explosions just by alternating between Overload and Incinerate. Once this was discovered, Atlases, Geth Primes, and Banshees became the only enemies to provide any challenge. All other shielded enemies found themselves being wiped out en masse.