Part 1 : we can grizzly, etc because we have type sample of grizzly. We have something to match to.
Part 2 : we don't know what bigfoot is. It is near impossible to tell "near human" from "degraded human" reliably with DNA.
I think the best we could do with environmental DNA is to say that there is a source of unknown DNA that is consistent making environmental degradation less likely because of consistency across samples.
The Marshall/Sanow study placed the 357 magnum Federal 125 grain JHP as the #1 one-shot man stopper.
The same 357 magnum loaded with Underwood 180 grain hard casts would be an outstanding choice for a sidearm in bear country.