The Xorda are currently engaged in an inter-galactic war with the Black Arms: an alien species made famous in the videogame Shadow The Hedgehog.
They posses a collective awareness, enabling all to experience what all other members of their species do. Given how they never speak of themselves in first person, only saying "The Xorda" rather than "I" or "We" and their identical appearance, it's likely that their species has no individuals and they function as a singular person. This would go a long way in explaining their behavior, if their species functions as one being, then it would only be logical that they would see the actions of one person to be the crime of the entire species, lacking the concept of individuality.
The Xorda from all appearances are vengeful in the extreme, for the wrongful death of one of their members they are willing to not only kill the person or persons responsible, but all of that species, and every living thing on the planet, and any living thing that might happen to evolve and share traces of the offender's species DNA eons later. To date the Xorda have shown no empathy for any species except their own.
The Xorda in general were purely aquatic in nature, as such their species possess numerous jellyfish-like attributes. Between twenty and thirty pink tentacles connected to a huge, purple "brain-sphere" with three gill-tubes on each side, two long fin-like flaps spanning across the membrane. A single, yellow eye is located between the two halves, seeing as it is never closed coupled with their aquatic nature they might not possess eyelids.
Attack on Earth
The Xorda's wrath was incurred upon Earth when an envoy they sent to it was captured, imprisoned, and dissected by human scientists. Outraged, the Xorda bombarded the planet with Gene Bombs, believing that all life had been wiped out. Unbeknownst to them, some survived, and eventually swelled to repopulate the planet. The energy of the bomb caused the mutation of many animal species into the anthropomorphic Mobians that now inhabit it, as well as the creation of Mobius' Chaos Emeralds. This latter fact was cast into doubt however when the source of this information—a 12,000 year old robot named Isaac—was revealed to have most of its data corrupted and/or erroneous when he was hacked into by Dr. Finitevus. (StH: #124, #125, #148, #165)
Attack on Mobius
The secrecy of continued life on Mobius was compromised when the Xorda discovered two ships heading for Mobius. Presumably they knew that there were Overlanders (humans) aboard as Hope Kintobor explained that they attacked them. Presumably they traced the ships to Mobius and realized that life had arisen again. Upon entering the Solar System, they nearly stumbled upon a ship from the Bem, a much more benevolent alien race, but were distracted by Shadow the Hedgehog. When they arrived, they delivered an ultimatum of destruction unto the people of Mobius, and also told them the truth about their world's origins. As if to demonstrate their power, they launched a devastating single-ship attack on Dr. Eggman's Eggman Empire. The ship was repulsed by Giga-Bot Prime, a giant robot created by Eggman that only Sonic's speed could power (presumably at that point in time, Eggman would surely have access to alternative power sources under normal circumstances). However, the Xorda had yet to play their trump card.
On Mobius' Southern Tundra, the Xorda revealed their final plan to eradicate the planet. A triangular device known as the Quantum Dial was set up with the purpose of tearing open a hole in reality, creating a black hole powerful enough to consume the planet and the entire solar system. It was assumed that such a large target would be easy to deal with, given that Station Square launched an immediate missile strike. However, the Quantum Dial possessed some kind of field that caused any construct within fifty feet to fall apart. Unwilling to give up without a fight, the various fighters of Mobius banded together, putting aside their differences to battle a common enemy. However, even with the amazing number of warriors aligned against them, the Xorda weapon was only vanquished after the timely resurrection of Knuckles the Echidna (who simultaneously caused the destruction of the weapon's defenses) and the seeming suicide attack of Sonic the Hedgehog upon the Quantum Dial, which caused the destruction of the device and teleported Sonic across the universe to the planet of Thoraxia.
The Xorda departed Mobius soon after they launched the Quantum dial leaving the entire planet for dead. Their declaration of war on Mobius was also the reason that the Bem did not pursue a vessel (which headed on a course back to Mobius via a Bem jumpgate) they believed to contain Ceneca 9009, the rogue scientist who built the De-Roboticizer. In truth, the vessel held Sonic, who had been beamed into space by the Quantum Dial's destruction. Unwittingly, the Xorda had inadvertently provided a safe journey home for their greatest hindrance. As the Bem pointed out that access to Mobius via their jumpgates was officially restricted on account of the Xorda having declared war on the planet - this would suggest the possibility that the Xorda are aware of their second failure to destroy all humanoid life on Mobius.
Some time after Sonic's return to Mobius, the Xorda became engaged in intergalactic warfare with the Black Arms, another warmongering species, which prevented the either race's return to Mobius. This resulted from the Black Arms' intent to consume Mobius' inhabitants, while the Xorda fully intended to destroy the entire planet, leading the two parties to war. Both races were later seen with their fleets engaged in combat above the Bem's war ravaged home world of Argentium. Around this same time, the Chaos Emeralds native to the Xorda homeworld were drawn to Mobius by Dr. Eggman's computer virus "son", A.D.A.M.
- The Xorda's name was once mistakenly spelled as Zorda.
- The Xorda are the only villains in the Sonic universe (perhaps the only ones in general) to refer to their enemies as "cute and furry."
- The war between the Xorda and the Black Arms served as a means of introducing the Black Arms into the comic continuity, while also explaining why they haven't arrived on Mobius yet. Ian Flynn explained that he was awaiting approval from Sega for the Black Arms to defeat the Xorda. However, the continuity reboot that followed the Worlds Collide crossover appears to have removed the Xorda from the series entirely, with the Black Arms arriving at Mobius without interference only to be met with defeat. However, the Xorda must have still bombarded Earth with their Gene Bombs, otherwise the Mobians would not exist in the new reality. However, there is the possibility that the Mobians evolved through other means, though this has not been elaborated on.
- The Xorda resemble the unarmored form of the Daleks of Doctor Who fame as tentacled creatures with a single eye and a large brain.