While previous Federation encounters with the Myhr'an indicated the Myhr'an had little expertise or scientific knowledge in cloning, encounters in 2372 proved large leaps and bounds in Myhr'an technology, including cloning. A Myhr'an clone, thought to be a dead Myhr'an, was brought aboard the USS Cantabrian for an autopsy from a derelict Myhr'an scout ship. The clone attacked med tech Nelson, killing him and taking his form. This clone was eventually hunted down and killed trying to escape. (Star Trek: The Cantabrian Expeditions: "Catalyst, Part One", "Catalyst, Part Two")
Performing an autopsy on a Myhr'an clone, Dr. Marie Bourget discovered internally the clone was comprised of a black "goo-like" substance with the ability to mimic and reflect normal bio-readings. (Star Trek: The Cantabrian Expeditions: "Catalyst, Part Two")
A Cantabrian away team, led by first officer Elizabeth Singh, discovered several Myhr'an incubation chambers aboard the Myhr'an super battle cruiser. Filled with thousands of clones at various stages of development, the chambers were jettisoned by the away team, killing the clones. (Star Trek: The Cantabrian Expeditions: "Catalyst, Part Two")
The away team also discovered that by downing a transmitter aboard the super battle cruiser, Mhyr'an clones ceased to function, as if they were remotely-controlled. (Star Trek: The Cantabrian Expeditions: "Catalyst, Part Two")
With so many clones available, the Myhr'an had vast resources at their fingertips. The ground forces at Canaileus Prime drove colony and Cantabrian defences thin on the ground. Eventually, with some desperate measures taken by Cantabrian and other Federation forces, the Myhr'an were driven back. (Star Trek: The Cantabrian Expeditions: "Oh, What a Lovely War")
While physically fighting Cantabrian captain Noah Wrightson and counselor Daniel Radke in late 2372, the Myhr'an commander admitted he'd help sell his people out to the M'Tar. They, in turn, supplied the initial clones, replacing important objectors, allowing the conspirators to eventually take over many key positions within the Myhr'an government. The Myhr'an commander -- one of the only pure Myhr'an left -- helped commit genocide against his own people in exchange for power. The vast majority of the Myhr'an population were now clones. (Star Trek: The Cantabrian Expeditions: "Deceptions")
- We assume the clones stopped functioning once the transmitter was destroyed for good in "Deceptions".