Bullsquids are bipedal, highly aggressive alien creatures that appears throughout the Black Mesa Research Facility due to the dimensional rift caused by the Resonance Cascade. They're able to survive, if not thrive, in environments that are unfriendly or even toxic to humans, including sewers and pools of radioactive, chemical, or biological waste. On Xen, Bullsquids are found drinking from Healing Pools. They're introduced in Half-Life’s third chapter, Unforeseen Consequences.
The body of a Bullsquid is vaguely similar in appearance to that of a small Theropod, with two short, muscular legs and a thick tail that tapers to a point, and with the head reminiscent to that of a squid, particularly the reef squid. The thorax abruptly joins the creature's head with no neck or other visible separation. A typical specimen stands roughly one meter tall and about two meters in length. Two slit-pupiled, white-beige and glossy eyes are mounted on either side of its head. The tail had a hooked claw at its tip, which explains the large amount of damage caused by the Bullsquid's spin attack.
The Bullsquid's most striking feature, however, is the collection of bright red, Cthulhu-esque, tentacle-like protrusions surrounding its mouth and allowing it to grasp prey. The Bullsquid can also charge an opponent with surprising speed and force; these two attributes are manifestly the cause of its portmanteau name, made of the words "bull" + "squid".
The Bullsquid's overall coloration is roughly comparable to that of a spotted cat: its skin is sandy brown and its upper surfaces has dark spots. The creature's skin appears to be slimy, similar to that of a terrestrial amphibian such as the frog.
Like most of the creatures found on Xen, Bullsquids are studied in Black Mesa's Sector E.
 Behavior and skills
The Bullsquid has an array of offensive capabilities. They display a very territorial disposition, as they have often been seen attacking other creatures and even members of their own species. They viciously attack Headcrabs, not stopping until all Headcrabs in their sight are eliminated, while they do not harm Houndeyes. They however do not attack, even when attacked themselves, when encountered during the Resonance Cascade in Half-Life and in the same map in Opposing Force. They are drinking from a Healing Pool both times, however, so it is likely that they are simply not aggressive while feeding or drinking or that they cannot see the player somehow.
At close range, a hostile Bullsquid will either maul its victim with its teeth, or suddenly spin around, delivering a powerful strike with its tail, often causing a gibbing. At long range, the Bullsquid is able to spit a toxic, bile-colored substance from its mouth, like the Antlion Worker. While not particularly accurate or fast, it causes moderate damage, even at very long range.
 Behind the scenes
|“||Ted remembers constructing one moster in particular: "That was actually back when I was talking with Gabe for the first time." Ted's legendary interview actually yielded in-game results: "I showed Gabe a picture before I even knew of the game at all, he just suggested that he wanted to do a game that was kind of like Stephen King's The Mist. So I read it, and there were some tentacle monsters in there, so I tried to think of anatomical structures that were intresting and notions that were interesting, and put together something that hadn't been seen before. So, I showed it to him and he said, 'Yes, let's buld it.' So it went into the game like that, and I think the geometry that went in was first-shot geometry and was never revised. I built it over the course of a couple of days and it went straightaway. This was something that just kind of appeared magically on its own: the bullsquid."||”|
|– Half-Life 2: Raising the Bar (uncorrected proof), page 30|
The Bullsquid is reminiscent of a creature created by Chuck Jones during the time when the game's codename was Quiver, the "Land Squid." Before being given its final name, it was also called the "Bullchicken"; it is still referred to under that name in the game files.
The first known Bullsquid model was beige-colored, similar to chicken, with black eyes. Its second iteration was bright yellow, with tiger/insect-like patterns, and red eyes.[a] Both had a less detailed mouth than that of the retail version, and more pointy tentacles.
In Online Gaming Review's early Half-Life Monster of the Week Feature preview, the Bullsquid was given the taxonomic designation "Gastropolypus toxophlegmata." It was described as a 1.8 meters (5.9 feet) tall and 3.6 meters (11.8 feet) long supreme predator, with its natural range and habitat remaining uncertain. Although the creature was said to bear signs of aquatic specialization, it was suggested that it had adapted to a terrestrial environment, as evidenced by its powerful limbs and characteristic neurotoxic (and reportedly psychoactive) spit. Of significance would be the Bullsquid's ferocious appetite (necessary to support its immense bulk) and an overwhelming libido. As a result, the creature would attempt to eat or mate with almost anything that crosses its path, without regard for species or any apparent reproductive necessity. The Bullsquid was said to be hermaphroditic, as indicated by dissection. Moreover, the toxic phlegm, lethal to terrestrial mammalian creatures, had been speculated to have aphrodisiac qualities to fauna of the Bullsquid's native environment.
 Half-Life 2
The Bullsquid was originally to appear in Half-Life 2. There are two versions of the creature known to exist.
In the first one, the Bullsquid has a deep maroon skin, yellow eyes with amphibian-like black pupils, and its toxic spit is green. Like the Houndeye, also cut from Half-Life 2, it was to be glimpsed during the original train ride to City 17 and appear in the Canals. Many can be found in the map "
d1_canals_02" in the playable leak, swimming underwater or attacking Headcrabs, with the sprite of the toxic spit does not showing properly.
According to Ted Backman, who designed the creature, when the developers first thought of the Bullsquid, they "had it running around the land and it wasn't very interesting. You saw it really far off, this big thing lumbering at you." It had proven not to be a consequential foe as it "was really easy to put your target on it and unload. Eventually, when it got close enough, you just dodged it." As a result, the developers decided to draw inspiration from nature, especially the "lunging predators that sit and wait, then leap out and grab at whatever they eat." By implementing a similar behavior, the Bullsquid took a more interesting form and the second version was born; it now sat in pools of water with most of its body covered up - only the eyes poked above the surface of the water. Resembling a 12 feet long crocodile, it was to wait for the player to get close, and then jump out and pull them in to devour them; it would also be able to swim and walk.
In an early version of the game, a slideshow revealing the events between Half-Life and Half-Life 2 was to be shown to Gordon at Eli's lab. In one of the images, Bullsquids were to be seen chasing a family from a suburban house.
According to series' writer Marc Laidlaw, they still exist in the Half-Life 2 continuity, being "around here somewhere". Bullsquids are mentioned by the Fisherman in Lost Coast, set in a level cut from the final game.
Yellow version from Half-Life Alpha.
 Half-Life 2 leak
 List of appearances
 Main games
- Half-Life: Opposing Force
- Half-Life: Blue Shift
- Half-Life: Decay
- Half-Life 2: Raising the Bar
- Half-Life 1997 Teaser (First appearance) (Non-canonical appearance)
- Half-Life: Day One
- Half-Life 2: Raising the Bar
- ↑ Half-Life 2 leak files
- ↑ 2.0 2.1 2.2 2.3 2.4 Half-Life 2: Raising the Bar
- ↑ Half-Life 2: Prima Official Game Guide
- ↑ Half-Life - Monster of the Week feature on Online Gaming Review (1997) (archived)
- ↑ WC mappack
- ↑ 6.0 6.1 Half-Life 2 leak
- ↑ Half-Life 2: Raising the Bar (uncorrected proof), page 259
- ↑ Info received from Valve on the ValveTime.net Forums (September 6, 2005)
- ↑ Game Design: Secrets of the Sages by Marc Saltzman (1999). Ted Backman: When creating the skin for the Bullsquid, I looked at many things for inspiration. I looked at the markings on sea slugs, the patterns on jungle cats, and many other unusual sources. When you create an image, you're communicating in a visual language; the vocabulary of that language is the shared set of images and experiences that all people know. So if you neglect to include pieces of our shared visual experience, you really aren't communicating at all. In the case of the Bullsquid, the coloration should cue most people that this is a poisonous animal. Yellow and black markings are nature's way of saying "stay away."