Liminal being

A liminal being is one that cannot be easily placed into a single category of existence. Associated with the threshold state of liminality, such beings represent and highlight the semi-autonomous boundaries of the social world.

Liminal beings are naturally ambiguous, challenging the cultural networks of social classification.

Victor Turner considered that liminal entities, such as those undergoing initiation rites, often appeared in the form of monsters, so as to represent the co-presence of opposites—high/low; good/bad—in the liminal experience.

Liminal personas are structurally and socially invisible, having left one set of classifications and not yet entered another.Mary Douglas has highlighted the dangerous aspects of such liminal beings, but they are also potentially beneficent. Thus we often find presiding over a ritual's liminal stage a semi-human shaman figure, or a powerful mentor with animal aspects, such as a centaur.

By extension, liminal beings of a mixed, hybrid nature appear regularly in myth, legend and fantasy.

A legendary liminal being is a legendary creature that combines two distinct states of simultaneous existence within one physical body. This unique perspective may provide the liminal being with wisdom and the ability to instruct, making them suitable mentors, whilst also making them dangerous and uncanny.

Many beings in fantasy and folklore exist in liminal states impossible in actual beings:

Hybrids (two species):

Both human and spirit by blood:

Both human and vegetable:

Both alive and dead:

Both human and machine:

Both human and alien:

...
Wikipedia