|“||Observe this Hornoad, unimportant creatures that jump up and down.||„|
In Metroid: Samus Returns, Hornoads are squat, green-colored creatures with wide, toothy mouths with no lips to cover them. The backs of their rounded bodies are studded with short spikes, and their only appendages are a stumpy tail and a pair of three-toed legs, the latter of which they use to hop around and launch themselves at enemies. Hornoads are relatively weak and, like all other creatures on SR388, release Aeion when killed, often with life energy and Missile ammo. They primarily live close to SR388's surface, though a tougher, red-skinned breed that can spit acid from a long range also inhabits the later Areas.
The Hornoads' original design in Metroid II is somewhat simpler. Their legs featured two clawed-toes only, one on each opposite ends. They had minuscule spikes on their backsides and had lips on their mouths; due to their artwork and in-game sprites never showing the creatures with their mouths open, it is unknown if they possessed any teeth. As a result, they had no projectile as well. Their bodies were more rounded and had no tail.
When an X Parasite infects a Hornoad, the former manipulates its host's DNA to alter its physiology and behavior, resulting in a Hornoad-X that is greatly intimidating, dangerous and driven by a need to further the spread of the X. In Metroid: Samus Returns, their teeth and dorsal spikes are larger and further pronounced, in addition to gaining an extra pair of eyes and warty, fuchsia-colored skin. They also acquire two organs in place of their tongues capable of spraying a yellow-colored substance not unlike their natural counterparts'. Overall, their appearance is grotesque in comparison.
The previous design of the Hornoad-X in Metroid Fusion did not possess any claws or spikes on its body while also lacking a second pair of eyes and a tail. Its back was covered in a mass of warts. Contrary to its recent appearance in Samus Returns, it featured lips which were often pulled back in order to bare its teeth and, along with the occasional twitching of its head in-game, gave the creature traits akin to rabies. Hornoad-X maintained its sickly fuchsia-colored skin, though its lower half had a stronger shade of blue.
Once the Hornoad-X is killed by outside means such as with Samus' arsenal, the X that inhabits the body leaves with a copy of the Hornoad's DNA and memories, allowing it to transform itself into a mimicry of the infected victim. However, the mimic is a replica of the described Hornoad-X above and not of the creature in an uninfected state. Thus, the many Hornoad-X encountered in Fusion are both infected Hornoads and X Parasites disguised as mimics. The Metroid Manga shows an X killing its Hornoad host immediately upon invading its body and replicates it mere moments later, demonstrating that the X will not always choose to live within a body and control it.
Hornoads had long existed on SR388 until a steady decline in the planet's entire wildlife population seemingly began with the appearance of the X Parasites, which slowly turned the planet into a graveyard of skeletons. The Metroid Manga shows a Hornoad fleeing from a group of X before getting infected by them, resulting in all of its soft organic tissue dissolving. With only its bones remaining, the X mimicked their victim soon afterwards.
When the Chozo race first came to SR388 with the intention of colonizing it, they had no knowledge of the danger that lived within and eventually came into conflict with the X. The Chozo Memories in Samus Returns shows this first encounter with the avian race fighting off a mass of X Parasites as they witness Hornoads being turned into Hornoad-X. The Chozo eventually created the Metroid species which began to carry out their purpose: to feed upon the virulent X along with all of their infected victims and mimicries (seen in the Chozo Memories with both X and Hornoad-X being eaten by the artificial lifeforms). Afterwards, the population of wildlife in general returned to a normal state and the X became extremely scarce, however the Metroids had become the new apex predator and would occasionally feed on SR388's other animals such as Hornoads (as shown during Samus Aran's mission on SR388).
Unfortunately, not knowing what the Metroids' purpose was on SR388 by anyone other than their extinct Chozo creators, Samus had been ordered to wipe out the artificial creatures, allowing the low population of X to multiply once more unchallenged. After she defeated Proteus Ridley and left the planet with the last living Metroid, a lone Hornoad is seen gnawing on Ridley's cast-off cybernetic claws before its attention is drawn to a fleeting X and is soon turned into a Hornoad-X.
Years later, when Samus was escorting Biologic's research team on SR388, she was attacked by a lone Hornoad-X in a cave. Upon being hit with a Missile, the parasite reverted to its gelatinous form and infected Samus, eventually leading to the removal of parts of her Power Suit and her inoculation with the Vaccine "Metroid". The portions of Samus' suit infected by the Hornoad-X would later become the SA-X. When Samus was sent to investigate an explosion at the Biologic Space Laboratories research station, she found the station overrun by the X. Hornoads were among the specimens infected and mimicked by X, and could be found on the Main Deck and in Sector 1. During Samus' battle against the SA-X, the latter transforms its own body into a monstrosity that shares features with a Hornoad's physiology, likely a result of the SA-X containing the DNA of the Hornoad that infected Samus in the first place.
In Fusion, uninfected Hornoads would continuously spawn from grey-green hives in the background, although no such structures were ever found on SR388.
- The Hornoad-X featured in the live action commercial for Fusion has a different design.
- The website data states that SR388 was Samus' first mission. This is not true, her Zero Mission on Zebes was. However, it is more likely the data is talking about her first mission pertaining to SR388.
- A Hornoad becoming being infected by the X can be seen in an ending cutscene of Samus Returns as an allusion to the upcoming events of Fusion.
- Additionally, Hornoads appear several times in the Chozo Memories from Samus Returns. The second memory shows a Chozo collecting an Aeion Orb dropped by a deceased Hornoad while another is being feasted on by a Gullugg. Another shows an X infecting a Hornoad and transforming into a Hornoad-X which is witnessed by the Chozo leading to the Metroids being developed. Another shows Larva Metroids under the direction of the Chozo preying on a group of Hornoad-X. A group of Hornoad can seen observing the arrival of the Galactic Federation Special Squadron ship in the opening as well. During a cutscene when Samus' Metroid Detector first beeps when it detects a nearby Metroid, a Hornoad is shown being attacked and preyed upon by a Larva Metroid which is implied to later mature into the first Alpha Metroid Samus encounters.
- Old Bird's statement about the Hornoad being an unimportant creature is ironic given that during Fusion Samus is almost killed after being infected by an X Parasite from a defeated Hornoad-X which she assumed was a normal Hornoad due to being unaware of the existence of the X at the time. In fact, SA-X is implied to possess Hornoad DNA in addition to Samus' as it transforms into what appears to be a Hornoad/Samus hybrid form during the climax of their battle on the B.S.L. station, which makes sense as SA-X was born as a result of the Hornoad-X infecting Samus' Power Suit components which where transferred to the station after they had been surgically removed resulting in the Station becoming infected after SA-X used a Power Bomb to escape the Quarantine Bay. This is even more ironic considering normal Hornoads are common enemies in Return of Samus and Samus Returns.
- In Samus Returns it is shown that Hornoads are apparently low on the food chain as a Metroid is shown preying on one and Chozo Memory 02 implies that Gullugg feed on them, though it is possibly they where just carrion feeding on deceased Hornoads as they are never shown actually preying on them during Samus' time on SR388 and they are shown coexisting with live healthy Hornoads. However this does not stop the X from selecting them as hosts, indicating they are strong enough for the X to target them.