In Mass Effect, the Milky Way galaxy is thriving with diverse life. There are species that haven't yet left their home planet, some that can reproduce asexually, and others that have worked to perfect AI technology.
Over the course of the Mass Effect games, Shepard takes on practically every kind of opponent in the galaxy, organic and otherwise. They must keep on top of their armor and upgrades to stand a chance. Even rare species like the yahg can be spotted! But which race is the most dangerous enemy to have? We take a look at the threat level that different species in Mass Effect pose.
16 The Keepers
The keepers are a race of insect-like creatures who live exclusively on the Citadel. They're interested in maintaining the space station, which means they're entirely disinterested in everything - and everyone - else.
They're not dangerous at all, except insofar as they help the reapers with their plan. Indeed, when the Citadel was first discovered, some insisted that the keepers were practically enslaved and attempted to compensate them, but the keepers wouldn't accept it.
15 The Yahg
The yahg are a sentient race from the planet Parnack. They are expert predators; when the Citadel first came into contact with them, they murdered the entire delegation. Afterward, the race was barred from interacting with Citadel space.
They aren't a space-faring race so, despite their natural abilities, they don't pose a significant threat. The only yahg you interact with during Mass Effect is the Shadow Broker. However, some pessimists (who feared the reapers would be successful in wiping out life) thought that the yahg could be the dominant race in the next cycle.
14 The Volus
The volus are an influential race in Citadel Space because of their extensive trading connections. Indeed, they developed an aptitude for economics when they realized that they couldn't compete with other races physically.
Volus largely rely on the turians to defend their space, though they do have their own airships. Most of them who do fight will employ some form of biotics, which can perform well, despite their size. It's far more dangerous to break a deal with a volus than to attack one.
13 The Vorcha
The vorcha are a short-lived race that have no significant presence in the galaxy on their own. Most Vorchawho leave their home planet wind up in mercenary gangs or other criminal activities; as a result, they can be found in seedy places like Omega.
The vorcha species is known to be especially aggressive - they primarily communicate via combat and other non-verbal forms, rather than language. As such, they are known to be a pain to deal with when encountered, but not a significant threat.
12 The Batarians
The batarians aren't on good terms with the Citadel Council, but also aren't interested in war. Their slave rings, drug running, and pirate gangs are much more profitable than a war would ever be.
Since the Citadel has no authority or presence on the batarian homeworld, little is known about their formal military - though it's thought to be insignificant compared to larger races'. They may make the galaxy a more dangerous place to live, but their collective strength isn't extraordinary.
11 The Quarians
Ever since they left their homeworld, Quarians have lived aboard a collection of ships called the "Migrant Fleet." This is a combination of civilian and military vessels - essentially anything useable - and even civilian vessels tend to be equipped with weapons.
Their technological know-how makes them dangerous enemies in the space age, but their sheer numbers are limited. As a result, most Quarians keep to themselves, seldom leaving the Fleet for good.
10 The Elcor
The elcor are a slow-moving species in every sense of the word. They are not the kind of people to rush into anything, let alone a fight. However, one shouldn't underestimate them - their enemies call them "living tanks" because of how their thick skin can shrug off attacks.
Relatively, though, elcor do not maintain a large military. They don't expect to get into a war without having some kind of forewarning and can seldom imagine anything they'd need to fight over anyway.
9 The Drell And Hanar
The drell are a mathematically insignificant race, by comparison to other species. When their home planet was destroyed, the hanar relocated as many as they could, but they could only do so much. Drell have no military or planet to call their own, now. However, they do significantly contribute to the hanar military forces.
The hanar have a small military of their own, but the drell support is what really gives it some efficiency. They try not to force drell into combat unless they can avoid it - the exception being the reaper invasion during Mass Effect 3.
8 The Krogan
Once, the krogan might have been among the most dangerous races in the galaxy. Since the genophage, though, their numbers have diminished significantly and the "throw wave after wave of troops at a problem" tactic isn't as viable.
Contemporary Battle Masters are seasoned krogans who know what it will take to succeed, and how far is too far. Since biotics are rare in their species, krogan place emphasis on other tactics, like psychological warfare and newly adapted weapons.
7 The Collectors
It's slightly unclear how large the collector forces are, since they are known to perform hit-and-run tactics and to lay in hiding in the Tartarus Debris Field. However, they have a clear military structure, with different units for specific jobs, so it's assumed that collectors are a significant force to be reckoned with.
However, based on Mordin Solus' observations, they lack any culture or creativity, so they cannot pull of creative maneuvers that other races might devise. They can only follow orders.
6 The Geth
The geth are a significant threat to peace in the galaxy. During their war against the quarians, they drove their opponents practically to extinction. Their intelligence is relative to the number of geth nearby, akin to a hive mind, but even a lone geth is incredibly dangerous.
Geth are, as Shepard notes in the games, excellent for ambushing tactics: "they don't move, they don't make noise, they don't even breath." They also care little for their physical bodies, since their consciousness will just enter another machine, making them unpredictable as opponents.
5 Humans
Humans are built for endurance. In the same vein, the human military is respected by other species for its flexibility, speed, and use of unconventional tactics. They have had the military in their culture for generations, and take the role seriously.
The combined human forces don't match up to any of the Council Races' fleets, but humans like to believe that their scrappy style could get them out of any tough situation. Plus, their technological advancements (including VI, artillery, and drones) help to compensate for their lack of numbers.
4 The Salarians
Salarians are worthy opponents due to their impeccable intelligence work, not the physical size of their forces. They firmly believe that wars should be won before they begin. Indeed, the salarian "Special Tasks Group" (STG) is a special recon unit that works outside the usual red tape - and went on to inspire the Spectre program.
Salarians may strike randomly and with no warning, but they are playing chess ten moves in advance before their enemies ever knew there was a game.
3 The Asari
The asari have one of the most significant militaries in the galaxy. Their military thrives on diversity. Asari from their communities form their own units and use the tactics they prefer, with no centralized structure. This allows them to be fluid and mobile, making up for what their troops lack in significant armour and weapons (which would weigh them down).
When the reapers attacked, the asari homeworld was actually one of the few to put up a good fight.
2 Turians
The turian civilization is a militaristic one to the core. All young turians are expected to serve, beginning at the age of 15, although many stay until their 30s, even if they were injured.
Discipline is worked into every young turian, and their boot camp involves special training on how to stay calm in a firefight. It's said that "you will only see a turian's back once he's dead." Most of the Citadel forces are made up of turian ships, and they take this responsibility seriously.
1 The Reapers
The Reapers, enormous metal creatures from the stars, are undoubtedly the most dangerous race in the Milky Way. The gun they fire is actually a weapon that spews molten metal at the speed of light.
They can also "indoctrinate" members of organic species into serving them. By harvesting the organic matter of their victims, they can create new reapers. Each one has a huge core made out of element zero. Even one reaper could kill millions and be practically unstoppable.