The following races are alien (i.e. not native) to Terra. This does not include the Ancients and Elders as even if the Sarkaz's claims that they are alien to Terra were true,[1][2] they had been adapted to Terra's environment and became part of its ecosystem.
Spirits
In the world of The Legend of Hei, Spirits (sometimes called Elfins) are basically natural spirits resembling to our world's yaoguai/yōkai/yojeong. They master supernatural powers that are not related to Originium Arts and could transform into many forms including becoming a human. Upon reaching a certain level, they could even evolve into a deified being.
Ah Gen is technically half-human and half-Spirit known as Xuanli.
Lynians
In the world of Monster Hunter, Lynians are short, intelligent creatures with mammalian features that are capable of comprehending human knowledge. There are only two subspecies, both ape-like or cat-like, with the latter being more peaceful to coexist with the humans in the MonHun world.
Miscellaneous
The following are non-human creatures (animals, plants, monsters, etc.) alien to Terra.
References
