"Let’s begin with the hulking monstrosity on the ground. Armed to the teeth (quite literally) with Kaiser Blades, this guy can sweep a Viking aside like it’s a twig in its path. I’ve seen them kill a score of marines with a single blow, and charge with such ferocity that they’ll even demolish one of those notorious ProtossForce Fields. I’m talking, of course, about the Ultralisk, and now we know everything there is to know about them."
"If you've never seen an ultralisk...it's bigger than a goddamn tank, and louder, and faster. Tall as four marines in full armor, and long enough that in the jungle you can be fighting the front end before you can even see the back of it coming out of the bush. It's got two pairs of scythes attached where wings might be on a dragon. They're called kaiser blades; I don't know why, but I've seen what they can do. They sweep through marine battle armor like it's tinfoil. You can unload a C-14 at an ultralisk until the barrel melts, and you'll only make it mad. Correction: madder. They're already mad. Ultralisks get out of bed mad and hungry. When they're done slashing you to bits, they stomp on the pieces of you before you're all the way dead."
Ultralisks are the most powerful ground strain the Swarm possesses and their DNA is the "final viable code" utilized by larvae. Living battering rams, ultralisks serve as the backbone of the Swarm, and serve as its siegebreaker. When dealing with these creatures, Dominionmarines are advised to maintain a wide perimeter and call in air support.
"But by far the biggest baddass of them all...is the aptly named ultralisk."
- A Dominion marine on the ultralisk's kaiser blades(src)
Fast for their size, ultralisks attack using large, bone-like scythes which protrude from their backs. Known as "kaiser blades", these scythes are nearly indestructible. Possessing monomolecular edges, these scythes are able to tear through most substances with ease, able to slice through armored vehicle and eviscerate entire squads of light infantry in just a few swipes. The density, bevel, and edges of these organic weapons are honed at the genetic level. By 2500 at least some ultralisks sported four kaiser blades as opposed to the usual two. By the Second Great War, four blades were the standard.
The ultralisk's size in of itself is also a weapon—they can charge with enough ferocity to even destroy protossforce fields.
Ultralisks possess an exceptionally thick carapace.Dominionscientists suspect that the larva's highly resistant carapace served as a template for enhancements to the creature. Preliminary tests on the carapace itself proved that the diamond-shaped, chitinous scales of the creature were combined with foreign compounds and organic tissue multiple times, resulting in very light plates with an unmatched level of hardness. A gene also exists within the ultralisk's genetic code that exists with the sole purpose of growing heavily armored copies of the beast's primary organs in random locations of its body. The brontolith's immune system was improved on for the ultralisk, allowing it to thrive in the most toxic and inhospitable environments the galaxy has to offer. The ultralisk's weak spots are located in its head (particularly the mouth and eyes), and its underbelly, and around the neck, as the plating there is thinner.
By the Brood War, prolonged exposure to vespene gas had resulted in an enhancement to the ultralisks' physical capabilities, among which was the evolution of a more hardened exoskeletal shell and the ability to carry out anabolic synthesis, alterations being made to the glands that produce endorphins and adrenal fluids. By the Second Great War, the strain had received substantial additions to its internal structure—a complex sensory system, an auxiliary nervous system, and specialized muscle fibers that expand or contract in reaction to stimuli. Through this, an ultralisk can maintain speed even with its hind legs severed.
Ultralisks birthed by the Leviathan Brood are terrifying vistages of spines and blades, monsters worthy of legend.
Ultralisks evolved from the docile brontolith; a creature that the ultralisk now bears little resemblance to. The brontoliths' genetic code was dissected, rebuilt and repurposed multiple times. Each phase of the process served to eliminate less desirable traits, as well as augment the creature's ability to withstand severe punishment. This included the creature's superb immune system. As a finishing touch to the ultralisk, the Swarm added the gene that would replace the creature's organs.
When terrans first encountered ultralisks on the battlefield, they observed that the creatures seemed to suffer balance issues, and were easily toppled by artillery fire or loss of limbs. By the Second Great War, "unstoppable" ultralisks had been observed. The additions to their internal structure were revealed, but the data offered very little in the way of finding a counter to the creature. Second Great War ultralisks were also noted to have a greater amount of Kaiser blades, as well as a higher amount of carapace armor.