First, assuming sasquatch exists only as a myth, its unfortunately seeming like a harbinger of the future. people are too quick to believe in something where there is no proof.

Both.

Interdimensional being.

If it exists, it's neither - it's merely a species of ape currently unknown to science and no more a relic or a harbinger than a gorilla, gibbon, chimpanzee or human.

My personal opinion, incidentally, is that the sasquatch, yeti and various other "ape men" probably don't exist; however, since new species, even fairly large ones, are still being discovered to this day, there's a possibility that they might in fact be real.