In the Z/X -Zillions of enemy X- TCG, they are represented by the "Eldritch Spawn" Token instead of their own separate Tribe.
Z/X Encyclopedia Entry
Dependent of the Cthulhu.
They are floating objects that appears after a Cthulhu passed by. It is unclear whether they are alive or only a substance, the expression "evil spirits of the mountains and rivers" is suitable for their appearance.
The concept of spawn is a recurring elements in the Cthulhu Mythos, with various entities producing their own kind of spawn or being the spawn of another entities. One of the artwork for the "Eldritch Spawn" itself is similar to the formless spawn.