The Efni egg is actually a chemical experiment gone wrong with a gemstone. Where did a chemical experiment go wrong, you ask? It is none other than at the Science and Research Center in Ark City.
The Efni is a living expression of the opal mineraloid and was created out of an accident at the Science and Research Center in Ark City. The SAR Center, once they had realized that they created something living from a stone, almost terminated the first Efni's life. But they refrained from doing this "for scientific purposes" to study the Efni in its living form.
Scientists and researchers, so far, have found that the Efni's temperament is actually quite agreeable but that there is nothing remarkable about the Efni outside of the fact that it was created from mixing toxic slime with heat and a mineral.
Efnis are able to be "owned" by Arkians but you cannot take one home with you. Efnis must stay at the Ark City Zoo in captivity at all times, so as not to disturb what the SAR Center calls the "natural ecosystem" of Ark.