Core Races

Core Races refer to dragons, elves, and humans.
Alone of the many mortal races in Scarterra, these three races were the only mortals created by all nine of the Nine working together whereas other mortals are created by one, two, three, or at most four of the Nine.
Only the Core Races are capable of creating healthy hybrid children with other races, though they can create hybrids with mortal races that are not Core Races.
Elf/human hybrids, elf/dragon hybrids, and human/dragon hybrids are the only hybrids that are not normally sterile. Because of this, most other hybrids are derogatively called mules.
Beyond the natural biological rules, humans, elves, and dragons commonly use their status as being Core Races to claim superiority over the other races.
Dragon hybrids are a fair bit more complicated because their magical nature and aptitude towards shape shifting circumvents normal fertility rules.
Satyr hybrids are a little bit more complicated. Satyrs are a derivative of elves, but they are also a different species in a way.

Exceptions that Prove the Rule

satyrs are techncially a subspecies of elves though elves rarely admit this. Satyrs can make viable offspring with humans and elves. In most cases, it is very hard to tell a half-satyr apart from a normal half-elf.
Supposedly dragon/kobold pairings have produced fertile offspring in the past but this has never been verified by a non-kobold. Nearly all kobolds claim this is possible because they are the spritual cousins of dragons. Few dragons agree to this. Many outsiders assume tales of half-dragon/half-kobolds are kobolds trying to tell tall-tales about their regal blood.

Type

Natural