Echo Echo is bullshit. This is known. You can't just say a lifeform is made of "living sound waves" and expect people to buy that without any sort of elaboration.
Well, as someone way too invested in explaining this shit, I'm here to elaborate on exactly that, so here we go!
Basic Principles Edit
Okay, let's get this out of the way first: Echo Echo is only kind of living sound waves, in the same way a human is just a lump of flesh; basically, that's part of the equation, but the full explanation is more nuanced than that.
The primary organism that is "Echo Echo" is a minuscule arthropod-like creature sealed inside a small "cockpit" of sorts in the silicon suits Sonorosians wear. This creature has no traditional eyes of its own, relying on the artificial lenses built into the suit to "see" its surroundings and convert the sight-based information into an audio format the creature is capable of interpreting. This system is comparable to echolocation, but is far more precise.
In regards to the creature's abilities, it has the ability to generate sound waves and manipulate them into specific patterns by scratching together specialized organs located on its tail and numerous leg-like tendrils. This appears to be a highly evolved form of similar mechanisms seen in Earth insects such as cicadas.
Using their abilities, these minuscule creatures are able to create "bodies" dozens of times their size by generating sound waves in extremely specific vibration patterns. The vibrations caused by these soundwaves are strong enough to repel the surface of whatever they come into contact with, giving them the illusion of solid mass despite being a waveform.
These vibrations are also how the creatures animate their silicon containment suits, which contain no motors of their own beyond those used to adjust the focus of the eye lenses. The suits are built around maximizing the efficiency of this method of locomotion, with the "headphones" on the head being used to transfer sound down to the "backpack", which contains a series of vibration-sensitive tubes that evenly distribute the sound waves throughout the entirety of the suit.
The suit has several ports on the arms and legs, with the arm ports containing extra lenses, effectively making them another set of "eyes", while the leg ports are wired into the suit's electronics, allowing connection to a given digital interface for maintenance purposes.
But What About the Cloning, CaT? Edit
I was getting to that but I couldn't think of a good segue to split up these sections so fight me.
Echo Echo's cloning ability is fairly simple to explain. The creature making up Echo Echo's 'true form', so to speak, is capable of rapid mitosis, allowing them to clone themselves in a similar manner to Ditto. Unlike Ditto, they have no psychic link connecting their bodies, making the clones fairly disposable.
The suits are designed to work with Echo Echo's cloning abilities, being internally covered in a specialized webbing that pulls in loose matter and energy from the surrounding area and converts it into material for another suit. This process is what creates Echo Echo's signature green glow during the cloning process.
But How Does the Suit Run, CaT? Edit
As I already mentioned, the suit has no motors dedicated to movement, so that eliminates a significant amount of necessary power to put into the electronics. However, the cloning webbing more than makes up for this in power consumption, leaving the demands of the suit too high for traditional battery power.
Fortunately(ish), the Sonorosians have pretty terrible digestion systems, and have to swallow heavily radioactive gastroliths in order to properly break down their food. This results in every Sonorosian not dead from starvation emitting enough excess radiation for their suits to run on. The suits are designed to fully contain this radiation, making it inconsequential to the creature's surroundings.
Fun Fact: Sonorosians, while significantly more resistant to radiation than most organic organisms, are not fully immune to it. Because of this, while the species has no actual aging mechanism, they will gradually deteriorate and die over time thanks to radiation poisoning.
This process of death ends up giving them a superficial similarity to lobsters, which do not age and will end up growing until they're simply too big to live and end up dying either because molting takes all of their energy or they're unable to molt anymore at all and get stuck in their own husks, resulting in them either starving to death or getting a deadly infection.
Nature's an asshole, ain't it, kids?