Crystalloid monster

Crystalloid monsters were believed to be an alien race from somewhere in outer space that lived billions of year before humans ever even existed, likely during the geological period known as the Hadean.

Their anatomy was unique in that they were made of a highly magnetic crystalline structure.

In fact, even if a body part was to break off, their magnetism would simply pull the severed limb back on.

They were considerably stronger than humans, and they were impervious to bullets.

They had the appearance of a crystal serpent with geometrically shaped head, torso, pelvis, and a tail; but no arms or legs of any kind, at least none that was visible. They simply moved about by creeping on the ground similar to a snake.

They also laid eggs to reproduce. Their eggs were black and impervious to drills capable of even cutting through diamond, meaning the shell of the egg was even harder than diamond. It should be noted however, that a double-dose of heat vision from Superboy and Krypto was able to penetrate the egg shell though.

Crystalloid mothers were very nurturing toward their young, and although they were generally not a hostile race, they were known to use violence when their young were threatened.

Appearance
The Adventures of Superboy
 * The Visitor from the Earth's Core