Selkie

Selkies are supernatural creatures capable of therianthropy, changing shape from human into that of a seal.

Selkies are said to have a strong connection to the sea, to such an extent that being separated from it at extended period of time can cause severe mental (and potentially even physical) pain.

Abilities
Therianthropy

Selkies possess the ability to shapeshift into a seal.

Allure

In their human forms, selkies are said to exhibit a supernatural beauty that makes them come across as especially alluring to ordinary humans.

Offspring & Breeding
The abilities of a selkie is genetic, and can be carried from parents to offspring. Two "pureblooded" selkies will always produce selkie offspring.

Humans and selkies can produce offspring together. Depending on the "purity" of their selkie parent, the offspring can either be human, selkie or, in rare cases, a hybrid (see Hylkies).

Hylkies
Hylkies is wide-spread term used to refer to human-selkie hybrids. Hylkies are humanoid creatures who possess certain seal-like traits. These include, but are not limited to, webbed toes and fingers, unusual skin coloration (such as green or blue-ish tinted skin) and a distinct smell of sea water or fish. Depending on the severity of these traits, they may appear more or less human.

Hylkies don't inherit any form of therianthropic ability, though are said to possess the same kind of unusual allure as their selkie ancestors.