Natural Selection 2 is the sequel to a 2001 Half-Life mod, which followed the same basic premise. However, it has been several years since the beginning of the Marina-Kharaa conflict, and both sides have developed and lost abilities, creating a significant contrast between the two games. Both were developed by Unknown Worlds Studios. NS2, however, is not a mod - it runs on an independently-developed engine.
The Natural Selection series contains examples of:
- Action Girl: Recent updates have added female marines.
- Art Shift: The Kharaa have undergone a significant art shift between NS1 and NS2. In the original, they appeared far more fleshy and organic. By NS2, they have become darker in color, with the exception of the Fade, which looks almost the same as it originally did. They have also gained significantly more armor on their heads and bodies. The Marines have also received an upgrade - their armor and structures are much more high-tech and smooth, contrasting the blockiness of the original.
- Assimilation Plot: Despite the Kharaa's modus operandi being 'assimilate other species and weaponize them,' care is taken to avert this. Marines cannot be assimilated by the bacterium, thanks to the wonders of Nanobot technology.
- Aura Vision: The Aliens' hive-mind gives them the ability to see friendly lifeforms and structures through walls, and with the proper upgrades or a parasite, marines as well.
- Air Vent Passage Way: Almost every map has at least one of these for Skulks, Lerks and Jetpackers to use. In some, normal marines can also get into after some parkour.
- Adaptive Ability: The Kharaa are incredibly versatile and adaptable. No matter how the Marines try to gain an edge, they seem to have a way to counter it, and often they adapt the marine's tactics in some way, such as with the Harvester, which functions in the same way as a Frontiersman Extractor to gather resources.
- Breath Weapon: The Gorge defends himself by spitting slime at his enemies. It's surprisingly effective at discouraging marines.
- Blood Knight: The Fade, which is said to be one of the most intelligent Kharaa lifeforms, seems to enjoy his job more than any other lifeform does, and shooting him just makes him mad, as the Fade Reveal trailer shows. You won't like him when he's angry.
- Bizarre Alien Biology: The Kharaa feature numerous bizarre traits. Special mention goes to the Skulk and Gorge, who share a trait - their lower jaws are actually two separate appendages, connected by a piece of stretchy flesh that acts as the bottom of their mouth.
- Continuity Nod: Several of the maps are updated shinier versions of maps from the original NS.
- Cool Tank: The Onos and Exosuit qualify for the Kharaa and Marines respectively.
- Cherry Tapping: As Alien, the Skulk, Lerk and Gorge can Cherry-tap with Parasite, Spike and Spit respectively. The Marines can cherry-tap with the are or a welder, or (formerly) the claw when in an exosuit.
- Deadly Gas: Both sides use those. Lerk has "Spores" that constantly drain health of marines in gas cloud (exosuits are safe), forcing them to retreat, constantly request medpacks from commander or bring flamethrower to burn the clouds. Marines have "nerve gas" grenades that are not lethal, merely draining armor of all aliens in range, softening them up for the kill with other weapons.
- Horn Attack: The Onos uses its center horn to gore marines and toss them around like ragdolls.
- Technology Porn: The Marines' structures and armor are beautifully rendered and smooth, unlike in the original, where they were highly blocky and heavy-duty.
- The Corruption: The Kharaa spread their infestation across the surrounding area, and assimilate other species into their genetic fold.
- Evolution Power-Up: The Kharaa thrive on this trope. Changing life-forms? Evolution. Getting an upgrade? Evolution!
- Evolutionary Levels: The Kharaa, again. Each 'level' qualifies as a lifeform. The Skulk and Fade appear to be related in some way, as they both share bladed limbs and a long muzzle with sharp teeth, and their movement animations are strikingly similar.
- Excuse Plot: The background for the conflict is unashamedly an excuse for the Marines and Aliens to savage eachother senseless. This hasn't stopped the fans from taking creative license with the intriguing background behind the Kharaa, though.
- The universe's details eventually became significantly more fleshed out with the release of Subnautica, which surprisingly shared the same universe despite being in a completely different genre.
- Flash Step: The Fade used to have an ability called shadow step to move around quickly. It can be upgraded to last as long as the Fade's energy pool does. It's modern variation, Blink, is similar but merely accelerates, not teleports.
- Finishing Stomp: The Onos can throw marines to the ground with an unlocked ability, at which point he can brutally crush their skull beneath his mighty spacecow weight. The Kharaa don't mess around, folks.
- From a Single Cell: How a Kharaa invasion starts. Apparently, even a small spore is enough to begin a serious infestation, as the Bacterium reproduces quickly and reacts viciously to threats.
- Gatling Good: The Minigun Exosuit has a chaingun on both arm that can reduce any hostiles to mush in seconds.
- It used to only have one minigun, complemented by rather useless claw, and could be upgraded to have another minigun. Now two miniguns is the only choice.
- Goomba Stomp: The Exosuit can goomba stomp eggs by merely moving on them, crushing them beneath its weight.
- Gameplay and Story Segregation: Despite the game's official Wiki stating that Fades have been observed warping through solid matter, they cannot do so for obvious reasons.
- Glowing Eyes of Doom: All of the Kharaa have had their eyes turned to an evil glowing orange color by the Bacterium.
- Hive Mind: The Kharaa share one, which is one of the major reasons they are so deadly.
- Idle Animation: The Aliens all have idle animations which they play when you're standing still. The Skulk and Fade pick their teeth with a claw, the Gorge yawns or licks at a decaying tooth, the Lerk stretches it's wings, and so on.
- I Shall Taunt You: The Marines can make snarky comments at the Aliens. The Aliens all have the ability to chuckle, and each lifeform has its own taunt.
- Keystone Army: The Kharaa depend on their Hives to live. If their Hives are destroyed, they all die instantly, along with the Infestation across the ship.
- Gameplay-wise, marines also lose if all command centers are lost. Presumably because they are automatically evacuated once it is clear they can't compete with local Kharaa presence.
- Kill It with Fire: The marine commander can research a flamethrower for his team. This weapon is great to scare away light enemies (such as skulks). However its main use is to clear out alien infestation and their organic buildings.
- Cluster grenades and welders also permit clearing out flammable buildings (usually whatever Gorge made) faster, however, former is limited use and latter is technically a melee weapon (actually just a repair tool) and thus of limited use.
- Lightning Bruiser: With the right upgrades, the Onos is a lightning bruiser, able to rush into an enemy base and completely wreck it in minutes.
- Mini-Mecha: The Marines can eventually research and purchase an enormous Exosuit with dual miniguns or railguns. It's as awesome as it sounds.
- More Teeth than the Osmond Family: The Skulk's main weapon is its enormous mouth full of very sharp teeth.
- Mouth Cam: The Skulk, Lerk and Gorge all play from a mouthcam perspective.
- Organic Technology: The Kharaa are adept at this, to the point that they're a match for the best equipped, best trained troops in the TSA without ever using a single piece of technology.
- One-Gender Race: None of the Kharaa appear to have a gender. Justified, however, given that the lifeforms in the Kharaa have been optimized for their roles, and the hive makes reproduction obsolete.
- Power Armor: The Marines could use Power Armor in the original NS. Second installments Exosuit is a Mini-Mecha instead.
- Pocket Dimension: The TSA speculates that the Fade is able to access one, explaining its ability to teleport around. The Fade can also send a large group of enemy soldiers/structures into the same zone for a short period of time, rendering them harmless, with the right upgrade.
- Plant Aliens: Some of the structures the Kharaa can build in both games strongly resemble plants.
- Preorder Bonus: Players who preordered the game receive a special Deluxe suit of armor for the Marines and get the official soundtrack and art for free. Players who preordered the special edition received the same, along with a suit of black marine armor. The Developers are debating on whether to include similar skinks for the Kharaa as part of the deluxe edition bonus.
- Robot Soldier: An update added set of skins for marines, "BMAC", that is basically this. Somehow they are still healed by medpacks and welders only fix their armour.
- Shared Universe: With Subnautica, also made by Unknown Worlds. Originally the name of the Alterra corporation on the Knife's blade in Subnautica was considered merely an easter egg, until a log file coded with a Caesar cipher and ASCII on the Habitat Update’s promotional webpage mentions “the Kharaa conflict," and as the game's wiki notes show
, the Carar bacterium was renamed to Kharaa to make the connection between the two more evident, and according to Word of God, the Kharaa aliens originated from that same bacterium. - Shotguns Are Just Better: Being able to instantly deal high damage at close range is extremely useful when most enemies want to come to said close range on their own volition. Shotgun is a very powerful tool in Frontiersmen's arsenal.
- Siege Engines: Automated Resonance Cannons ("ARC") are future versions of this. They shoot sonic waves that can delete Kharaa buildings and work through walls (albert at very limited range). They are useful for when Frontiersmen can't just shoot enemy buildings without dying, but they cost lot of resources and can't hurt alien players, requiring protection to work.
- Kharaa has access to Contamination that ensures marines can't just bunker in their last base for any significant time. Either marines counterattack and disable Contamination, or lose their base to constant anti-structure damage of ever-spawning alien buildings.
- Slave Race: Technically, every playable lifeform counts, given that all of them have been assimilated into the Kharaa by the Bacterium. It's unknown which, if any, were sentient when they were assimilated, but the Fade in particular is speculated to have been.
- Scenery Porn: The Kharaa's infestation and structures, while squicky, are beautiful in their own, odd way.
- Trailers Always Lie: Subverted in that most gameplay features shown in the game's promotional videos are included, but disappointingly, it is not possible to impale an enemy's marines and redirect his attacks on his allies as in the Exosuit reveal trailer.
- Unstable Equilibrium: Thanks to RTS part, whoever gains economical advantage early on has much, much better chances to win their fight later. Team resources gained are spent onto researches that passively boost your players' stats, as well as onto support buildings. This, along with field abilities that also cost resources, allows to win their fight and have control over territory, gaining even more resources.
- We Have Reserves: Either the marines are somehow being saved from death when they die, or their commanders are EXTREMELY liberal about how many lives they're prepared to lose to hold onto the installation. Justified with the Kharaa, who are simply assimilated back into the bacterium and born again as a new lifeform when they sustain fatal damage.
- Worker Unit: The Gorge falls under this category, being the Kharaa's engineer/medic, as his healing spray can speed up the building process for structures placed by the Alien Commander, and he can place clumps of infestation to act as a barricade or grow spikey plants that send barbs into nearby marines.
- The entirety of the marine team also falls under this category, given that they need to build structures their commander places, unlike the Kharaa, who's structures will grow without aid from a Gorge, albeit slowly.
- The marine commander also has access to a robotics bay later in the game that builds directly controlled units called MAC. They are completely automated and will build and repair anything near them.
- You Will Be Assimilated: Every single playable lifeform, and some of the structures, are extraterrestrial species which have been assimilated by the Kharaa. The Marines, fortunately, cannot be assimilated, as the nanobots in their bodies kill the bacterium if their suits are breached by it.
- Zerg Rush: If the Commander can coordinate his team into a rush, they can end the round in record time by swarming the enemy base and destroying their Command Chair/Hive.
- This is pretty much justified with the Kharaa, since they are an alien race with small, very fast, four-legged, wall climbing units known as skulks, who are extremely weak early-game and must work together to take down marines.
