In the Pacific Northwest, follow Bigfoot in the copter as he moves through the trees. Be careful because he may trick you. You have to follow him until he reaches the caves.
Yes, you can find proof of The Jersey Devil, Bigfoot, Nessie, and the Chupacabra. (see related question)
first you have to find all the other cryptids then you go in the helicoptor to the new location and follow him to his cave
A gorilla
You get the Island Medallion after you prove the existence of three of the four cryptids, and rescue Bigfoot from the evil Gretchen Grimlock. (see related question)
You don't. However, you will later follow Bigfoot as he travels through the trees in the Pacific Northwest.
Not Bigfoot's footprint, but possibly that of the Yeti (a similarly described creature). It is above the monastery on a trail to the upper left. You need a photo of the footprint in the snow.
He is in the Pacific Northwest, where he lives in a cave. Once you have confirmed the other 3 cryptids, you can go there and follow him in the helicopter.
just wait for it to move the follow with helicopter
You can't, because it never appears. You do find Bigfoot at the end of the quest. All you can do at the Himalayas is get the lantern from the monastery and a photo of a footprint high up on the mountain. This is not enough proof. When you prove the other three cryptids, Mews will send you after Bigfoot instead.
just keep following from a distance
When you first start the island and you get the paper about Mews needing the evidence of ONE cryptid to get your reward, you end up needing to search for 4: Bigfoot, the Loch Ness Monster, the Chupacabra, and the Jersey Devil.
After you have confirmed the other three cryptids (Nessie, Chupacabra, and the Jersey Devil), and brought back the inconclusive footprint from the Himalayas, Mews will send you in pursuit of Bigfoot, which is similar to the Yeti.