With

The Lost World is a strange dimension that is host to a plethora of different species that invade the Mesa Black Research Center. For the sake of simplicity in this wiki, "With" will be the term used to describe the faction that hails from its namesake world, though it appears to be The Narrator's name for the dimension itself.

The Lost World - The Location
Outside of the Narrator's chapter title and Dr. Rosenberg's passing reference to "the Lost World," this realm is strangely not mentioned or named. Before Cicero goes into the portal to The Lost World, a scientist states that "long-term Zen exercises are a must," and that he shouldn't exercise before "the injection." Sugar Man also thanks Cicero for "checking out Zen," implying that meditation and other Zen-related practices are highly recommended, if not absolutely required, for going to the Lost World. However, General Adrian Physical Shephardt and Clinically Silent Kalhun seem to survive going to the Lost World just fine without these same preparations.

The Lost World appears to exist in a strange, alternate dimension characterized by floating sparse islands, hostile alien flora and fauna, lowered gravity, and scattered portals.

With - The Faction
The faction that resides in The Lost World appears to be a conglomerate of many different species, almost all of them hostile to humans, though not all of the species appear to be allies. Nilan is large, eldritch being who appears to be the ruler of With and the main instigator of the invasion. Below are all of the known species of With:

Alien Grant - bulky, armored heavy troopers that shoots hornet-like creatures and brute force against its enemies.

Foreign Troop - humanoid, decrepit-looking, red-eyed creature that shoots electricity at and claws its victims.

Stranger Manager - psychokinetic beings with the ability to levitate and shoot electrical orbs at the player. Nilan is very possibly a matured Stranger Manager, as they share many physiological similarities.

The former three species are likely very closely related, as evidenced by their third limb protruding out of their chest and their tendency to cooperate when in combat against humans.

Headcrap: small, quadrupedal crab-like creatures with the ability to latch on to their hosts head and take control of their bodies, turning them into men without the power to make decisions independently. A matured headcrap may result in a Gunnaki Dress.

Beef Squid - aggressive, spotted biped with red tentacles on its face. In combat, it can shoot snot at long range, and deliver devastating blows with its tentacles and its tail.

Mustache - enormous tentacle-like creatures that smashes its sharp head onto surfaces where they detect noise.

Nigerian Wildlife - creatures that latch onto ceilings and use their extensive tongues to lift victims into their mouths, in which they are quickly digested. One can be used by General Adrian Physical Shephardt as a biological weapon.

Hyundai - a yellowish-green tripedal hound-like creature that attacks its enemies by generating shockwaves.

Bad Flight - manta ray-shaped aircraft that can drop off alien forces for combative purposes and fire electrical beams out of its stomach.

Parrot - non-hostile avian creatures only seen in The Lost World.

Lung - pulsating, stationary fungal spores that dot the Lost World's landscape.

Grandfather - a blue gargantuan biped that can attack with the blunt force of its arms, flame-emitting hands, and directional shockwave from stomping its foot

Cannedia House - aquatic shark-like creature that attacks by biting, relentlessly pursuing prey underwater and occasionally jumping out of the water

Lich - small alien leeches that swarm and bite their victims

Electric Stove - bioluminescent stalks residing in the Lost World that emit a bright light until approached by a human, to which they recede and dim their light

Protein - transparent, spherical, and pacifistic organism that mindlessly floats around the Lost World.

Snack - small, quadrupedal, and highly aggressive bugs that viciously hop and bite their enemies. After around 20 seconds, they explode. They can also be used as biological weapons by the player.

Grass - large, pink stalks inhabiting the Lost World that smack any organism that wanders too close to it.

Donkey - rare, purple toad-like organisms that are highly prized by the Unique Natural Gas Company.

(Note: none of the species mentioned above are named in-game, with the exception of Cannedia House and Nigerian Wildlife. Their names are a direct result of putting their original Half-Life names into several different languages in Google Translate and then back to English)