Zyglak were a bipedal reptilian race. The zyglak was one of the first species created by the Great Beings, a result of remnants left over from the creation of the Matoran being exposed to energized protodermis. Those remnants that did not become krana became zyglak, but the Great Beings had no use for this new species, particularly after it was discovered that they were plague carriers. They were shunned and hated wherever they went and nursed a deep resentment toward Matoran, whom they saw as occupying the favored position in the universe that should have been theirs. Zyglak extended their desire for revenge to any krana or Bohrok they encountered and anyone who spoke the language of the Matoran. They killed Toa Lesovikk's fellow Toa and an unknown number of other Toa and Matoran over the millennia. Zyglak relied on crude tools and weapons but made up for it with their natural advantages, including almost complete invulnerability to elemental attack and their ability to spread an organic protodermis-destroying disease through contact.
The Zyglak were a reptilian race accidentally created by the Great Beings out of the remains of the process that brought the first Matoran villagers to life. The Great Beings were seeking to create intelligent organisms called krana, but found that some of the material they used turned to Zyglak instead. Shunned by their creators and hated and feared throughout the universe, the bitter, savage Zyglak retreated to the dark places. There they waited, brooding over their fate and hating the Matoran and all who honored Mata Nui. Those who encountered them rarely survived.
The leavings from the process that brought the Matoran into being were used to create the Zyglak.
Zyglak were reptilian beings known as "the Great Beings' mistakes." They were notoriously violent and destructive and hated the Great Spirit Mata Nui and anything associated with him. They were outcasts. A group of Zyglak allied with Spiriah had a small fleet of ragtag sea vessels within the Matoran universe. Their ships were extremely ugly, slapped together from remnants and wreckage and barely sea-worthy.
The Zyglak were a humanoid, reptilian race created by mistake when the Great Beings were making the first krana. Having no use for the Zyglak, the Great Beings rejected them. Although they were allowed to live in the Matoran universe, they had no role to play, no place to call home, and no reason for being. Over time, they grew bitter and hostile and became a danger to all who lived. Zyglak took to hiding in ruins and other dark places where few ever ventured. Zyglak were immune to elemental attack, could spread a plague on contact, and carried spears and knives that could destroy any target on contact.
Zyglak were taller than Toa.
Zyglak were amphibious.
Zyglak hated everything they saw as being loyal to the Matoran or Mata Nui.
The zyglak weren't organic.
The zyglak lived in places no one else wanted to be, such as the flooded remains of the original Pit and the subterranean recesses of Voya Nui. They didn't necessarily all live outside the domes.